Show events at their real time on days the clocks change (#387) (#393)

On the day the clocks change, the day, 3-day and week views placed events by the time elapsed since midnight, so every event after the change sat an hour off. A 14:45 event on 25 October showed at 15:45. Blocks are now placed by wall clock.

When the clocks go back, 02:00 to 03:00 happens twice, and a wall-clock time alone can't say which of the two it means. This branch keeps track of it:

- The event form holds each time as a `FormTime`, the wall clock plus its UTC offset when that time is in the repeated hour. Validation and saving read the real instants from it, so a span ending in the repeated hour is valid and switching between the two passes is saved.
- A time picked in the form or dragged with a resize handle goes back to the event's original pass when it's set back to its original time. Otherwise it moves in the direction it was moved, stays after the start, and takes a pass the grid can draw where it was dropped.
- A drop onto a repeated time lands on the first pass, unless the event was already on the second.
- A block that runs into the repeated hour from before it is drawn to 03:00, and its label shows its real end.
- The editor, the event details and the pinned zone's "local time" line add the zone abbreviation (CEST or CET) to a time in the repeated hour.
- A recurring series that starts in the repeated hour keeps its pass when it's edited.

Also in this PR:

- `ZoneSource`, provided through Hilt, gives the timeline, the event form and reschedules the device zone. The timeline lays its pages out again when the zone changes.
- A drafted block (#153) opens the form at its exact start and end.
- A day move onto the spring-forward day keeps its wall-clock start, so moving a weekly series there is still offered for all events.

## Testing

The 1,258 unit tests pass. The instrumented suite has the same two failures as `release/v2.23.0` (`CalendarRepositorySmokeTest` and `PermissionScreenTest`), so nothing new.

I also checked it by hand on an emulator in Europe/Berlin, with the clock moved to each DST day:

- 25 October: the event from the issue (14:45, Europe/Brussels) is drawn at 14:45. A run from 02:10 CEST to 02:20 CET is drawn to 03:00 and labelled with its real end.
- Pulling the end of a 02:30 to 03:30 CET event up to 02:45 saves 02:45 CET, after its start.
- Pulling the end of a 01:00 CEST to 04:00 CET event up to 02:15 saves 02:15 CEST, and the block stays where it was dropped.
- 29 March: a 01:00 to 04:00 run and a 14:00 event both sit at their own times.

Picking times in the form and moving a series in the month view are covered by unit tests only.

Closes #387

Co-authored-by: Jean-Luc Makiola <business@jeanlucmakiola.de>
Reviewed-on: https://codeberg.org/jlmakiola/calendula/pulls/393

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapper.kt

@@ -1,15 +1,19 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.calendula.domain.instantIn
+import kotlinx.datetime.toKotlinTimeZone
 import android.provider.CalendarContract
 import de.jeanlucmakiola.calendula.domain.AccessLevel
 import de.jeanlucmakiola.calendula.domain.Availability
 import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventForm
+import de.jeanlucmakiola.calendula.domain.FormTime
 import de.jeanlucmakiola.calendula.domain.EventStatus
 import de.jeanlucmakiola.calendula.domain.ics.ParsedIcsEvent
 import de.jeanlucmakiola.calendula.domain.nearestTo
 import kotlinx.datetime.toJavaLocalDate
 import kotlinx.datetime.toJavaLocalDateTime
+import kotlinx.datetime.toJavaZoneOffset
 import java.time.Duration
 import java.time.Instant
 import java.time.ZoneId
@@ -48,8 +52,8 @@ internal fun EventForm.toWriteTimes(zone: ZoneId): EventWriteTimes = if (isAllDa
 } else {
     val writeZone = writeZone(zone)
     EventWriteTimes(
-        dtStartMillis = start.toJavaLocalDateTime().atZone(writeZone).toInstant().toEpochMilli(),
-        dtEndMillis = end.toJavaLocalDateTime().atZone(writeZone).toInstant().toEpochMilli(),
+        dtStartMillis = start.instantIn(writeZone.toKotlinTimeZone()).toEpochMilliseconds(),
+        dtEndMillis = end.instantIn(writeZone.toKotlinTimeZone()).toEpochMilliseconds(),
         timezone = writeZone.id,
     )
 }
@@ -75,7 +79,7 @@ private fun EventForm.writeZone(deviceZone: ZoneId): ZoneId = if (isAllDay) {
 private fun EventForm.anchorLocal(): JavaLocalDateTime = if (isAllDay) {
     start.date.toJavaLocalDate().atStartOfDay()
 } else {
-    start.toJavaLocalDateTime()
+    start.dateTime.toJavaLocalDateTime()
 }
 
 /**
@@ -181,7 +185,8 @@ internal fun buildEventUpdateValues(
 
     // A zone change counts as a time change even when the wall-clock is
     // untouched: the same 09:00 in another zone is a different instant, so
-    // DTSTART has to move with it.
+    // DTSTART has to move with it. So does a switch between the two passes of
+    // the fall-back hour, which each [FormTime] carries (#387).
     val timesChanged = updated.start != original.start ||
         updated.end != original.end ||
         updated.isAllDay != original.isAllDay ||
@@ -209,15 +214,23 @@ internal fun buildEventUpdateValues(
         // is a different offset from the series anchor's whenever a DST boundary
         // sits between them, or whenever the zone itself changed. Working in wall
         // clock keeps "09:00" meaning 09:00 at both ends.
-        val seriesLocal = Instant.ofEpochMilli(seriesDtStartMillis)
-            .atZone(original.writeZone(zone)).toLocalDateTime()
+        val seriesZoned = Instant.ofEpochMilli(seriesDtStartMillis).atZone(original.writeZone(zone))
+        val seriesLocal = seriesZoned.toLocalDateTime()
         val wallClockShift = Duration.between(original.anchorLocal(), updated.anchorLocal())
         val shifted = seriesLocal.plus(wallClockShift)
         // An all-day series anchor must sit on a UTC midnight. A pure day move
         // already lands there (both ends are midnights), but *switching* a
         // recurring event to all-day shifts by a time-of-day too, so snap.
         val newSeriesLocal = if (updated.isAllDay) shifted.toLocalDate().atStartOfDay() else shifted
-        val newSeriesStart = newSeriesLocal.atZone(updated.writeZone(zone))
+        // A wall clock the fall-back hour repeats keeps the anchor's own pass, or,
+        // when the anchor is the edited occurrence itself, the pass the form now
+        // holds: a bare wall clock would always take the earlier one (#387).
+        val pass = if (seriesLocal == original.anchorLocal()) {
+            updated.start.offset?.toJavaZoneOffset()
+        } else {
+            seriesZoned.offset
+        }
+        val newSeriesStart = ZonedDateTime.ofLocal(newSeriesLocal, updated.writeZone(zone), pass)
         put(CalendarContract.Events.DTSTART, newSeriesStart.toInstant().toEpochMilli())
         put(CalendarContract.Events.DTEND, null)
         put(CalendarContract.Events.RRULE, updated.rrule)

app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesSyncEngine.kt

@@ -8,6 +8,7 @@ import de.jeanlucmakiola.floret.reminders.ReminderOverride
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.domain.Availability
 import de.jeanlucmakiola.calendula.domain.EventForm
+import de.jeanlucmakiola.calendula.domain.FormTime
 import de.jeanlucmakiola.calendula.domain.RecurrenceFreq
 import de.jeanlucmakiola.calendula.domain.SimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.contacts.ContactSpecialDate
@@ -212,8 +213,8 @@ class SpecialDatesSyncEngine @Inject constructor(
             calendarId = calendarId,
             title = title,
             isAllDay = true,
-            start = start,
-            end = start,
+            start = FormTime(start),
+            end = FormTime(start),
             reminders = reminderCtx.resolveAllDay(calendarId),
             availability = Availability.Free,
             rrule = YEARLY_RRULE,

app/src/main/java/de/jeanlucmakiola/calendula/data/di/DataModule.kt

@@ -21,7 +21,9 @@ import de.jeanlucmakiola.calendula.data.contacts.SpecialDatesCalendarSpec
 import de.jeanlucmakiola.calendula.data.reminders.ProviderReminderInstanceSource
 import de.jeanlucmakiola.calendula.data.reminders.ReminderInstanceSource
 import de.jeanlucmakiola.calendula.data.time.AndroidTodaySource
+import de.jeanlucmakiola.calendula.data.time.AndroidZoneSource
 import de.jeanlucmakiola.calendula.data.time.TodaySource
+import de.jeanlucmakiola.calendula.data.time.ZoneSource
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.Dispatchers
 import javax.inject.Singleton
@@ -69,6 +71,12 @@ abstract class DataBindModule {
     abstract fun bindTodaySource(
         impl: AndroidTodaySource,
     ): TodaySource
+
+    @Binds
+    @Singleton
+    abstract fun bindZoneSource(
+        impl: AndroidZoneSource,
+    ): ZoneSource
 }
 
 @Module

app/src/main/java/de/jeanlucmakiola/calendula/data/time/ZoneSource.kt

@@ -0,0 +1,51 @@
+package de.jeanlucmakiola.calendula.data.time
+
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+import android.content.IntentFilter
+import androidx.core.content.ContextCompat
+import dagger.hilt.android.qualifiers.ApplicationContext
+import kotlinx.coroutines.channels.awaitClose
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.callbackFlow
+import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.onStart
+import kotlinx.datetime.TimeZone
+import javax.inject.Inject
+
+/**
+ * The zone the device is in. Every screen that turns wall clock into instants
+ * reads it from here, so the timeline, the event form and a saved move use the
+ * same zone (#387).
+ */
+interface ZoneSource {
+    /** The device's zone, re-emitted whenever it changes. */
+    val zone: Flow<TimeZone>
+
+    /** The device's zone right now. */
+    fun current(): TimeZone
+}
+
+/** Follows the system's zone broadcast. */
+class AndroidZoneSource @Inject constructor(
+    @ApplicationContext private val context: Context,
+) : ZoneSource {
+
+    override val zone: Flow<TimeZone> = callbackFlow {
+        val receiver = object : BroadcastReceiver() {
+            override fun onReceive(context: Context, intent: Intent) {
+                trySend(Unit)
+            }
+        }
+        val filter = IntentFilter(Intent.ACTION_TIMEZONE_CHANGED)
+        ContextCompat.registerReceiver(context, receiver, filter, ContextCompat.RECEIVER_NOT_EXPORTED)
+        awaitClose { context.unregisterReceiver(receiver) }
+    }
+        .onStart { emit(Unit) }
+        .map { current() }
+        .distinctUntilChanged()
+
+    override fun current(): TimeZone = TimeZone.currentSystemDefault()
+}

app/src/main/java/de/jeanlucmakiola/calendula/domain/EventForm.kt

@@ -4,7 +4,7 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.toInstant
+import kotlinx.datetime.UtcOffset
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Instant
 
@@ -17,8 +17,8 @@ data class EventForm(
     val calendarId: Long?,
     val title: String = "",
     val isAllDay: Boolean = false,
-    val start: LocalDateTime,
-    val end: LocalDateTime,
+    val start: FormTime,
+    val end: FormTime,
     /**
      * The zone [start]/[end] are wall-clock values in, or null to follow the
      * device — null is not "no zone", it is "whichever zone the device is in
@@ -70,6 +70,19 @@ data class EventForm(
     val attendees: List<EventAttendee> = emptyList(),
 )
 
+/**
+ * One end of a form's span: a wall-clock [dateTime] in the form's zone, and the
+ * [offset] it was read at when the fall-back hour repeats that wall clock — both
+ * of the hour's instants share one [LocalDateTime] (#387). Null everywhere else,
+ * so a time changed and changed back compares equal again. A time picked by hand
+ * gets its pass from [repicked]; one without an offset reads as the earlier
+ * pass. One value, so a time never changes without its pass. See [toFormTime].
+ */
+data class FormTime(val dateTime: LocalDateTime, val offset: UtcOffset? = null) {
+    val date: LocalDate get() = dateTime.date
+    val time: LocalTime get() = dateTime.time
+}
+
 /**
  * One editable guest: the user controls the [email] (the identity we dedup and
  * write on), an optional display [name], and whether they're [optional] rather
@@ -145,16 +158,15 @@ fun EventDetail.toEditForm(beginMillis: Long, endMillis: Long, zone: TimeZone):
             ?.takeIf { runCatching { TimeZone.of(it) }.isSuccess }
     }
     val formZone = pinnedZone?.let { TimeZone.of(it) } ?: zone
+    val begin = Instant.fromEpochMilliseconds(beginMillis)
+    val finish = Instant.fromEpochMilliseconds(endMillis)
     val (start, end) = if (instance.isAllDay) {
-        val startDate = Instant.fromEpochMilliseconds(beginMillis)
-            .toLocalDateTime(TimeZone.UTC).date
-        val endExclusive = Instant.fromEpochMilliseconds(endMillis)
-            .toLocalDateTime(TimeZone.UTC).date
+        val startDate = begin.toLocalDateTime(TimeZone.UTC).date
+        val endExclusive = finish.toLocalDateTime(TimeZone.UTC).date
         val endDate = maxOf(startDate, LocalDate.fromEpochDays(endExclusive.toEpochDays() - 1))
-        LocalDateTime(startDate, LocalTime(9, 0)) to LocalDateTime(endDate, LocalTime(10, 0))
+        FormTime(LocalDateTime(startDate, LocalTime(9, 0))) to FormTime(LocalDateTime(endDate, LocalTime(10, 0)))
     } else {
-        Instant.fromEpochMilliseconds(beginMillis).toLocalDateTime(formZone) to
-            Instant.fromEpochMilliseconds(endMillis).toLocalDateTime(formZone)
+        begin.toFormTime(formZone) to finish.toFormTime(formZone)
     }
     return EventForm(
         calendarId = instance.calendarId,
@@ -221,20 +233,18 @@ fun EventDetail.toEditSnapshot(beginMillis: Long, endMillis: Long, zone: TimeZon
     )
 
 /**
- * The form's times as they land in [target] — what a pinned event's wall-clock
- * actually means where the user is standing. Null when there's nothing to
- * disambiguate: an unpinned event (already in [target]), one pinned to [target]
- * itself, an all-day event (no zone), or an unparseable pinned zone.
+ * Whether this form's times mean something else in [target] — a timed event
+ * pinned to another zone. False when there's nothing to disambiguate: an
+ * unpinned event (already in [target]), one pinned to [target] itself, an
+ * all-day event (no zone), or an unparseable pinned zone.
  *
- * The form edits a pinned event in its own zone, so this is what lets the UI
- * show the other side of the pair rather than making the user do the arithmetic.
+ * The form edits a pinned event in its own zone, so this is what tells the UI
+ * to show the other side of the pair rather than making the user do the arithmetic.
  */
-fun EventForm.timesIn(target: TimeZone): Pair<LocalDateTime, LocalDateTime>? {
-    if (isAllDay) return null
-    val pinned = timezone?.let { runCatching { TimeZone.of(it) }.getOrNull() } ?: return null
-    if (pinned.id == target.id) return null
-    return start.toInstant(pinned).toLocalDateTime(target) to
-        end.toInstant(pinned).toLocalDateTime(target)
+fun EventForm.isPinnedAwayFrom(target: TimeZone): Boolean {
+    if (isAllDay) return false
+    val pinned = timezone?.let { runCatching { TimeZone.of(it) }.getOrNull() } ?: return false
+    return pinned.id != target.id
 }
 
 /**
@@ -254,9 +264,19 @@ fun EventForm.populatedFields(): Set<EventFormField> = buildSet {
     if (attendees.isNotEmpty()) add(EventFormField.Attendees)
 }
 
-fun EventForm.problems(): Set<EventFormProblem> = buildSet {
+/**
+ * What stops this form from saving. A timed span is checked as instants in the
+ * form's zone (else [deviceZone]): one ending in the fall-back hour's repeat can
+ * end on an earlier wall clock than it starts (#387).
+ */
+fun EventForm.problems(deviceZone: TimeZone): Set<EventFormProblem> = buildSet {
     if (calendarId == null) add(EventFormProblem.NoCalendar)
-    val endsTooEarly = if (isAllDay) end.date < start.date else end < start
+    val endsTooEarly = if (isAllDay) {
+        end.date < start.date
+    } else {
+        val zone = resolvedZone(deviceZone)
+        endInstant(zone) < startInstant(zone)
+    }
     if (endsTooEarly) add(EventFormProblem.EndBeforeStart)
     // An UNTIL before the first day would make the provider generate zero
     // occurrences — the event would silently vanish from every view.

app/src/main/java/de/jeanlucmakiola/calendula/domain/EventShift.kt

@@ -3,10 +3,19 @@ package de.jeanlucmakiola.calendula.domain
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.TimeZone
+import kotlinx.datetime.UtcOffset
+import kotlinx.datetime.offsetAt
 import kotlinx.datetime.plus
 import kotlinx.datetime.toInstant
+import kotlinx.datetime.toJavaLocalDateTime
+import kotlinx.datetime.toJavaZoneId
+import kotlinx.datetime.toJavaZoneOffset
+import kotlinx.datetime.toKotlinUtcOffset
 import kotlinx.datetime.toLocalDateTime
+import java.time.ZonedDateTime
 import kotlin.time.Instant
+import kotlin.time.toJavaInstant
+import kotlin.time.toKotlinInstant
 
 /**
  * The zone this form's wall-clock times mean, matching what the data layer
@@ -15,6 +24,114 @@ import kotlin.time.Instant
 fun EventForm.resolvedZone(deviceZone: TimeZone): TimeZone =
     timezone?.let { runCatching { TimeZone.of(it) }.getOrNull() } ?: deviceZone
 
+/**
+ * This wall-clock time in [zone], at [preferred] when the fall-back hour repeats
+ * it and that is one of its two offsets — otherwise the earlier one (#387).
+ */
+fun LocalDateTime.resolveIn(zone: TimeZone, preferred: UtcOffset?): Instant =
+    ZonedDateTime.ofLocal(toJavaLocalDateTime(), zone.toJavaZoneId(), preferred?.toJavaZoneOffset())
+        .toInstant().toKotlinInstant()
+
+/** Whether this instant's wall clock in [zone] is one the fall-back hour repeats. */
+fun Instant.inRepeatedHour(zone: TimeZone): Boolean {
+    val zid = zone.toJavaZoneId()
+    return zid.rules.getTransition(java.time.LocalDateTime.ofInstant(toJavaInstant(), zid))?.isOverlap == true
+}
+
+/**
+ * [at]'s offset in this zone when its wall clock is one the fall-back hour
+ * repeats, else null: elsewhere the wall clock alone already names the instant.
+ * What a [FormTime.offset] holds (#387).
+ */
+fun TimeZone.repeatedHourOffsetAt(at: Instant): UtcOffset? = if (at.inRepeatedHour(this)) offsetAt(at) else null
+
+/** This instant as a [FormTime] in [zone], keeping its pass of a repeated hour. */
+fun Instant.toFormTime(zone: TimeZone): FormTime = FormTime(toLocalDateTime(zone), zone.repeatedHourOffsetAt(this))
+
+/** This time as an instant in [zone], on its kept pass of a repeated hour. */
+fun FormTime.instantIn(zone: TimeZone): Instant = dateTime.resolveIn(zone, offset)
+
+/**
+ * This edge of an event moved to [picked] by hand — a picker or a resize handle —
+ * as a [FormTime] in [zone]. A time in the spring-forward gap moves on to the
+ * real one, as the provider would read it. A wall clock the fall-back hour
+ * repeats has two instants; which one it means (#387):
+ * - [original]'s, when [picked] is the wall clock the event was opened with, so
+ *   a time changed and changed back is the time it was;
+ * - else the one that moves the edge in the direction the user moved it:
+ *   earlier than this edge's instant when [picked] is before [shownAt] (where
+ *   the edge was on screen), later when after;
+ * - kept within [notBefore]..[notAfter] (the other edge), and to the ones
+ *   [drawable] accepts — where the screen can show it — when any fit.
+ */
+fun FormTime.repicked(
+    picked: LocalDateTime,
+    zone: TimeZone,
+    shownAt: LocalDateTime = dateTime,
+    original: FormTime? = null,
+    notBefore: Instant? = null,
+    notAfter: Instant? = null,
+    drawable: (Instant) -> Boolean = { true },
+): FormTime {
+    if (picked == dateTime && picked == shownAt) return this
+    val offsets = zone.toJavaZoneId().rules.getValidOffsets(picked.toJavaLocalDateTime())
+    if (offsets.isEmpty()) return FormTime(picked).instantIn(zone).toFormTime(zone)
+    if (offsets.size == 1) return FormTime(picked)
+    val passes = offsets.map { picked.toInstant(it.toKotlinUtcOffset()) }.sorted()
+    val bounded = passes.filter { (notBefore == null || it >= notBefore) && (notAfter == null || it <= notAfter) }
+        .ifEmpty { passes }
+    val fitting = bounded.filter(drawable).ifEmpty { bounded }
+    if (original?.dateTime == picked && original.offset != null && original.instantIn(zone) in fitting) return original
+    val from = instantIn(zone)
+    val chosen = when {
+        picked < shownAt -> fitting.lastOrNull { it < from }
+        picked > shownAt -> fitting.firstOrNull { it > from }
+        else -> null
+    } ?: fitting.minBy { (it - from).absoluteValue }
+    return chosen.toFormTime(zone)
+}
+
+/** The form's start as an instant in [zone]. */
+fun EventForm.startInstant(zone: TimeZone): Instant = start.instantIn(zone)
+
+/** The form's end as an instant in [zone]. */
+fun EventForm.endInstant(zone: TimeZone): Instant = end.instantIn(zone)
+
+/** The form's timed span set to these instants, read in [zone]. */
+fun EventForm.withTimes(start: Instant, end: Instant, zone: TimeZone): EventForm =
+    copy(start = start.toFormTime(zone), end = end.toFormTime(zone))
+
+/**
+ * The form pinned to [zoneId] (null: the device). A kept pass of a repeated hour
+ * was one of the old zone's, so it goes when the zone the times mean changes.
+ */
+fun EventForm.withTimezone(zoneId: String?, deviceZone: TimeZone): EventForm {
+    val pinned = copy(timezone = zoneId)
+    if (pinned.resolvedZone(deviceZone) == resolvedZone(deviceZone)) return pinned
+    return pinned.withoutKeptPasses()
+}
+
+/**
+ * The form with its start picked by hand, keeping its length. A repeated hour's
+ * pass is [repicked]: [original] is the start the event was opened with.
+ */
+fun EventForm.withStart(start: LocalDateTime, zone: TimeZone, original: FormTime? = null): EventForm {
+    val span = endInstant(zone) - startInstant(zone)
+    val startAt = this.start.repicked(start, zone, original = original).instantIn(zone)
+    return withTimes(startAt, startAt + span, zone)
+}
+
+/**
+ * The form with its end picked by hand. A repeated hour's pass is [repicked],
+ * kept after the start where it can be: [original] is the end the event was
+ * opened with.
+ */
+fun EventForm.withEnd(end: LocalDateTime, zone: TimeZone, original: FormTime? = null): EventForm =
+    copy(end = this.end.repicked(end, zone, original = original, notBefore = startInstant(zone)))
+
+/** The form with no kept passes: its times as the wall clock alone says them. */
+fun EventForm.withoutKeptPasses(): EventForm = copy(start = FormTime(start.dateTime), end = FormTime(end.dateTime))
+
 /**
  * The form moved so it starts at [newStart], keeping its **instant** duration —
  * a recurring event's length travels to the provider as `DURATION`, so keeping
@@ -26,11 +143,8 @@ fun EventForm.resolvedZone(deviceZone: TimeZone): TimeZone =
 fun EventForm.shiftedTo(newStart: Instant, deviceZone: TimeZone): EventForm {
     if (isAllDay) return this
     val zone = resolvedZone(deviceZone)
-    val span = end.toInstant(zone) - start.toInstant(zone)
-    return copy(
-        start = newStart.toLocalDateTime(zone),
-        end = (newStart + span).toLocalDateTime(zone),
-    )
+    val span = endInstant(zone) - startInstant(zone)
+    return withTimes(newStart, newStart + span, zone)
 }
 
 /**
@@ -43,21 +157,21 @@ fun EventForm.shiftedByDays(days: Int, deviceZone: TimeZone): EventForm {
     val newStart = LocalDateTime(start.date.plus(days, DateTimeUnit.DAY), start.time)
     if (isAllDay) {
         return copy(
-            start = newStart,
-            end = LocalDateTime(end.date.plus(days, DateTimeUnit.DAY), end.time),
+            start = FormTime(newStart),
+            end = FormTime(LocalDateTime(end.date.plus(days, DateTimeUnit.DAY), end.time)),
         )
     }
     val zone = resolvedZone(deviceZone)
-    val span = end.toInstant(zone) - start.toInstant(zone)
-    return copy(start = newStart, end = (newStart.toInstant(zone) + span).toLocalDateTime(zone))
+    val span = endInstant(zone) - startInstant(zone)
+    val startAt = FormTime(newStart, start.offset).instantIn(zone)
+    // The start keeps the wall clock it was moved to, even one the spring-forward
+    // gap skips, so a recurring series still sees a whole-day move.
+    val movedStart = startAt.toFormTime(zone).takeIf { it.dateTime == newStart } ?: FormTime(newStart)
+    return copy(start = movedStart, end = (startAt + span).toFormTime(zone))
 }
 
 /** The form with new start and end, each in the form's own zone — a resize. All-day is untouched. */
 fun EventForm.resizedTo(newStart: Instant, newEnd: Instant, deviceZone: TimeZone): EventForm {
     if (isAllDay) return this
-    val zone = resolvedZone(deviceZone)
-    return copy(
-        start = newStart.toLocalDateTime(zone),
-        end = newEnd.toLocalDateTime(zone),
-    )
+    return withTimes(newStart, newEnd, resolvedZone(deviceZone))
 }

app/src/main/java/de/jeanlucmakiola/calendula/domain/InsertEventForm.kt

@@ -4,7 +4,6 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Duration.Companion.hours
 import kotlin.time.Instant
@@ -46,16 +45,12 @@ fun buildInsertEventForm(
             ?.let { Instant.fromEpochMilliseconds(it).toLocalDateTime(TimeZone.UTC).date }
             ?.let { exclusive -> maxOf(startDate, LocalDate.fromEpochDays(exclusive.toEpochDays() - 1)) }
             ?: startDate
-        LocalDateTime(startDate, LocalTime(9, 0)) to LocalDateTime(endDate, LocalTime(10, 0))
+        FormTime(LocalDateTime(startDate, LocalTime(9, 0))) to FormTime(LocalDateTime(endDate, LocalTime(10, 0)))
     } else {
-        val startTime = beginMillis
-            ?.let { Instant.fromEpochMilliseconds(it).toLocalDateTime(zone) }
-            ?: nextFullHour(now, zone)
-        val endTime = endMillis
-            ?.let { Instant.fromEpochMilliseconds(it).toLocalDateTime(zone) }
-            ?.takeIf { it >= startTime }
-            ?: (startTime.toInstant(zone) + 1.hours).toLocalDateTime(zone)
-        startTime to endTime
+        val startAt = beginMillis?.let(Instant::fromEpochMilliseconds) ?: nextFullHour(now)
+        val endAt = endMillis?.let(Instant::fromEpochMilliseconds)?.takeIf { it >= startAt }
+            ?: (startAt + 1.hours)
+        startAt.toFormTime(zone) to endAt.toFormTime(zone)
     }
     return EventForm(
         calendarId = null,
@@ -71,8 +66,8 @@ fun buildInsertEventForm(
     )
 }
 
-private fun nextFullHour(now: Instant, zone: TimeZone): LocalDateTime {
+/** The first full hour after [now]: may roll into the next day before midnight. */
+internal fun nextFullHour(now: Instant): Instant {
     val hourMillis = 3_600_000L
-    val rounded = (now.toEpochMilliseconds() / hourMillis + 1) * hourMillis
-    return Instant.fromEpochMilliseconds(rounded).toLocalDateTime(zone)
+    return Instant.fromEpochMilliseconds((now.toEpochMilliseconds() / hourMillis + 1) * hourMillis)
 }

app/src/main/java/de/jeanlucmakiola/calendula/domain/TimeZoneCatalog.kt

@@ -157,14 +157,36 @@ fun timeZoneOptionOf(
  * the offset isn't stated twice in ICU's spelling and ours.
  */
 fun zoneDescriptor(option: TimeZoneOption): String {
-    val abbrev = option.shortName
-    return when {
-        abbrev == "UTC" -> "UTC"
-        abbrev.startsWith("GMT") -> formatGmtOffset(option.offsetMinutes)
-        else -> "$abbrev · ${formatGmtOffset(option.offsetMinutes)}"
-    }
+    val name = zoneAbbreviation(option)
+    val statesOffset = option.shortName == "UTC" || option.shortName.startsWith("GMT")
+    return if (statesOffset) name else "$name · ${formatGmtOffset(option.offsetMinutes)}"
 }
 
+/**
+ * [option]'s short name on its own — "CEST", "UTC" — with an offset-shaped one
+ * normalised to our GMT form, as [zoneDescriptor] spells it.
+ */
+fun zoneAbbreviation(option: TimeZoneOption): String = abbreviation(option.shortName, option.offsetMinutes)
+
+/**
+ * Zone [id]'s abbreviation [at] an instant, as [zoneAbbreviation] spells it,
+ * without the localized long name a whole [TimeZoneOption] would look up. Null
+ * for an id the tz database can't parse.
+ */
+fun zoneAbbreviationAt(
+    id: String,
+    locale: Locale,
+    at: Instant,
+    regionOf: (String) -> String? = { null },
+): String? {
+    val zone = runCatching { ZoneId.of(id) }.getOrNull() ?: return null
+    val shortName = resolveAbbreviation(zone.id, zone.rules.isDaylightSavings(at), locale, regionOf)
+    return abbreviation(shortName, zone.rules.getOffset(at).totalSeconds / 60)
+}
+
+private fun abbreviation(shortName: String, offsetMinutes: Int): String =
+    if (shortName.startsWith("GMT")) formatGmtOffset(offsetMinutes) else shortName
+
 /**
  * [options] matching [query], best matches first; a blank query returns the list
  * unchanged. Matching is accent- and case-insensitive and treats underscores as

app/src/main/java/de/jeanlucmakiola/calendula/domain/ics/ParsedIcsForm.kt

@@ -1,6 +1,8 @@
 package de.jeanlucmakiola.calendula.domain.ics
 
 import de.jeanlucmakiola.calendula.domain.EventForm
+import de.jeanlucmakiola.calendula.domain.FormTime
+import de.jeanlucmakiola.calendula.domain.toFormTime
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
@@ -24,9 +26,9 @@ fun ParsedIcsEvent.toEventForm(zone: TimeZone): EventForm {
         val startDate = this.start.toLocalDateTime(TimeZone.UTC).date
         val endExclusive = this.end.toLocalDateTime(TimeZone.UTC).date
         val endDate = maxOf(startDate, LocalDate.fromEpochDays(endExclusive.toEpochDays() - 1))
-        LocalDateTime(startDate, LocalTime(9, 0)) to LocalDateTime(endDate, LocalTime(10, 0))
+        FormTime(LocalDateTime(startDate, LocalTime(9, 0))) to FormTime(LocalDateTime(endDate, LocalTime(10, 0)))
     } else {
-        this.start.toLocalDateTime(zone) to this.end.toLocalDateTime(zone)
+        this.start.toFormTime(zone) to this.end.toFormTime(zone)
     }
     return EventForm(
         calendarId = null,

app/src/main/java/de/jeanlucmakiola/calendula/ui/CalendarHost.kt

@@ -96,6 +96,7 @@ import kotlinx.datetime.TimeZone
 import kotlinx.datetime.toLocalDateTime
 import kotlin.coroutines.cancellation.CancellationException
 import kotlin.time.Clock
+import kotlin.time.Instant
 
 /**
  * Holds the top-level view back stack (spec M1) and swaps between the calendar
@@ -240,18 +241,24 @@ fun CalendarHost(
     var heldCreateIso by remember { mutableStateOf<String?>(null) }
     var createStartMinutes by rememberSaveable { mutableStateOf<Int?>(null) }
     var heldCreateMinutes by remember { mutableStateOf<Int?>(null) }
-    // A drafted block's end (#153), in minutes from the start day's midnight.
-    var createEndMinutes by rememberSaveable { mutableStateOf<Int?>(null) }
-    var heldCreateEndMinutes by remember { mutableStateOf<Int?>(null) }
-    val onCreateSpan: (LocalDate, Int?, Int?) -> Unit = { date, startMinutes, endMinutes ->
+    // A drafted block's start and end (#153) as epoch millis. Instants rather than
+    // minutes into a day, so the form opens at the times drawn even across a DST
+    // change (#387).
+    var createDraftMillis by rememberSaveable { mutableStateOf<LongArray?>(null) }
+    var heldCreateDraftMillis by remember { mutableStateOf<LongArray?>(null) }
+    fun openCreate(date: LocalDate, startMinutes: Int?, draftMillis: LongArray?) {
         heldCreateIso = date.toString()
         createDateIso = date.toString()
         heldCreateMinutes = startMinutes
         createStartMinutes = startMinutes
-        heldCreateEndMinutes = endMinutes
-        createEndMinutes = endMinutes
+        heldCreateDraftMillis = draftMillis
+        createDraftMillis = draftMillis
+    }
+    val onCreateEvent: (LocalDate, Int?) -> Unit = { date, startMinutes -> openCreate(date, startMinutes, null) }
+    val onCreateDraft: (Instant, Instant) -> Unit = { start, end ->
+        val date = start.toLocalDateTime(TimeZone.currentSystemDefault()).date
+        openCreate(date, null, longArrayOf(start.toEpochMilliseconds(), end.toEpochMilliseconds()))
     }
-    val onCreateEvent: (LocalDate, Int?) -> Unit = { date, startMinutes -> onCreateSpan(date, startMinutes, null) }
 
     // Edit form (v1.3) — reuses the detail screen's occurrence key; for
     // recurring events the form itself asks for the write scope at save
@@ -387,8 +394,8 @@ fun CalendarHost(
                 createDateIso = iso
                 heldCreateMinutes = null
                 createStartMinutes = null
-                heldCreateEndMinutes = null
-                createEndMinutes = null
+                heldCreateDraftMillis = null
+                createDraftMillis = null
                 onWidgetNavConsumed()
             }
             null -> {}
@@ -604,7 +611,7 @@ fun CalendarHost(
                     onOpenDay = onOpenDay,
                     onEventClick = onEventClick,
                     onCreateEvent = onCreateEvent,
-                    onCreateSpan = onCreateSpan,
+                    onCreateDraft = onCreateDraft,
                 )
                 ViewScreen.Month -> MonthScreen(
                     onOpenDay = onOpenDay,
@@ -693,7 +700,7 @@ fun CalendarHost(
                 EventEditScreen(
                     initialDateIso = iso,
                     initialStartMinutes = createStartMinutes ?: heldCreateMinutes,
-                    initialEndMinutes = createEndMinutes ?: heldCreateEndMinutes,
+                    initialDraft = createDraftMillis ?: heldCreateDraftMillis,
                     onClose = { createDateIso = null },
                     onSaved = { createDateIso = null },
                     onManageCalendars = { showCalendars = true },

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/RescheduleViewModel.kt

@@ -3,6 +3,7 @@ package de.jeanlucmakiola.calendula.ui.common
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
+import de.jeanlucmakiola.calendula.data.time.ZoneSource
 import de.jeanlucmakiola.calendula.data.calendar.CalendarRepository
 import de.jeanlucmakiola.calendula.data.calendar.NoSuchEventException
 import de.jeanlucmakiola.calendula.data.di.IoDispatcher
@@ -16,6 +17,8 @@ import de.jeanlucmakiola.calendula.domain.parseSimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.problems
 import de.jeanlucmakiola.calendula.domain.realignRecurrence
 import de.jeanlucmakiola.calendula.domain.resizedTo
+import de.jeanlucmakiola.calendula.domain.endInstant
+import de.jeanlucmakiola.calendula.domain.startInstant
 import de.jeanlucmakiola.calendula.domain.resolvedZone
 import de.jeanlucmakiola.calendula.domain.shiftedByDays
 import de.jeanlucmakiola.calendula.domain.shiftedTo
@@ -128,6 +131,7 @@ sealed interface MoveOutcome {
 class RescheduleViewModel @Inject constructor(
     private val repository: CalendarRepository,
     @IoDispatcher private val io: CoroutineDispatcher,
+    private val zoneSource: ZoneSource,
 ) : ViewModel() {
 
     private val _scopePrompt = MutableStateFlow<MoveScopePrompt?>(null)
@@ -317,7 +321,7 @@ class RescheduleViewModel @Inject constructor(
             return null
         }
 
-        val zone = TimeZone.currentSystemDefault()
+        val zone = zoneSource.current()
         val original = detail.toEditForm(request.beginMillis, request.endMillis, zone)
         val shifted = when (val target = request.target) {
             is MoveTarget.Start -> original.shiftedTo(target.instant, zone)
@@ -329,7 +333,7 @@ class RescheduleViewModel @Inject constructor(
 
         // The UNTIL check is deferred to the write, which knows how far the move
         // reaches and so which date has to clear it.
-        if ((shifted.problems() - EventFormProblem.RecurrenceEndsBeforeStart).isNotEmpty()) {
+        if ((shifted.problems(zone) - EventFormProblem.RecurrenceEndsBeforeStart).isNotEmpty()) {
             _outcome.value = MoveOutcome.Failed
             return null
         }
@@ -495,8 +499,7 @@ class RescheduleViewModel @Inject constructor(
     private fun resizedEndMillis(prepared: PreparedMove): Long? {
         if (prepared.request.target !is MoveTarget.Span) return null
         val form = prepared.updated
-        return form.end.toInstant(form.resolvedZone(TimeZone.currentSystemDefault()))
-            .toEpochMilliseconds()
+        return form.endInstant(form.resolvedZone(zoneSource.current())).toEpochMilliseconds()
     }
 
     /**
@@ -508,8 +511,7 @@ class RescheduleViewModel @Inject constructor(
         return if (form.isAllDay) {
             form.start.date.atStartOfDayIn(TimeZone.UTC).toEpochMilliseconds()
         } else {
-            form.start.toInstant(form.resolvedZone(TimeZone.currentSystemDefault()))
-                .toEpochMilliseconds()
+            form.startInstant(form.resolvedZone(zoneSource.current())).toEpochMilliseconds()
         }
     }
 

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/TimeFormat.kt

@@ -1,7 +1,12 @@
 package de.jeanlucmakiola.calendula.ui.common
 
 import androidx.compose.runtime.staticCompositionLocalOf
+import de.jeanlucmakiola.calendula.domain.inRepeatedHour
+import de.jeanlucmakiola.calendula.domain.zoneAbbreviationAt
+import kotlinx.datetime.TimeZone
 import java.time.LocalTime
+import kotlin.time.Instant
+import kotlin.time.toJavaInstant
 import java.time.format.DateTimeFormatter
 import java.util.Locale
 
@@ -68,3 +73,15 @@ fun formatHourLabel(hour: Int, is24Hour: Boolean, locale: Locale): String =
     }
 
 private const val MINUTES_PER_DAY = 1_440
+
+/**
+ * [formatted] — [instant]'s time in [zone] — with the zone's abbreviation after
+ * it ("2:30 AM CEST") when the fall-back hour repeats that time, the one case
+ * where the time alone doesn't say which instant it is (#387).
+ */
+fun withRepeatedHourZone(formatted: String, instant: Instant, zone: TimeZone, locale: Locale): String {
+    if (!instant.inRepeatedHour(zone)) return formatted
+    val abbreviation = zoneAbbreviationAt(zone.id, locale, instant.toJavaInstant(), ::icuTimeZoneRegion)
+        ?: return formatted
+    return "$formatted $abbreviation"
+}

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/TimelineDrag.kt

@@ -46,8 +46,16 @@ import androidx.compose.ui.unit.dp
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.domain.EventInstance
+import de.jeanlucmakiola.calendula.domain.instantIn
+import de.jeanlucmakiola.calendula.domain.repeatedHourOffsetAt
+import de.jeanlucmakiola.calendula.domain.repicked
+import de.jeanlucmakiola.calendula.domain.toFormTime
+import de.jeanlucmakiola.calendula.domain.resolveIn
 import de.jeanlucmakiola.calendula.ui.week.MINUTES_PER_DAY
 import de.jeanlucmakiola.calendula.ui.week.TimedBlock
+import de.jeanlucmakiola.calendula.ui.week.minutesPast
+import de.jeanlucmakiola.calendula.ui.week.wallClockEndMinutes
+import de.jeanlucmakiola.calendula.ui.week.wallClockMinutes
 import de.jeanlucmakiola.floret.identity.rememberReduceMotion
 import de.jeanlucmakiola.floret.locale.currentLocale
 import kotlinx.coroutines.delay
@@ -55,13 +63,14 @@ import kotlinx.coroutines.flow.StateFlow
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.atStartOfDayIn
+import kotlinx.datetime.UtcOffset
 import kotlinx.datetime.plus
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
 import kotlin.math.roundToInt
+import kotlin.time.Duration
 import kotlin.time.Duration.Companion.minutes
 import kotlin.time.Instant
 
@@ -297,12 +306,13 @@ internal fun draftStartMin(minutes: Float): Int =
 
 /** The part of [draft] on [date] as a full-width block, or null if none of it falls there. */
 internal fun draftBlock(draft: EventInstance, date: LocalDate, zone: TimeZone): TimedBlock? {
-    val start = draft.start.toLocalDateTime(zone)
-    val end = draft.end.toLocalDateTime(zone)
+    // Clipped to the day the way the grid lays out events, so it's drawn the same across a DST change (#387).
     // The end is exclusive, so a draft ending at midnight belongs to the day before.
-    if (start.date > date || end.date < date || (end.date == date && end.time == LocalTime(0, 0))) return null
-    val startMin = if (start.date < date) 0 else start.time.toSecondOfDay() / 60
-    val endMin = if (end.date > date) MINUTES_PER_DAY else end.time.toSecondOfDay() / 60
+    val start = maxOf(draft.start, date.atStartOfDayIn(zone))
+    val end = minOf(draft.end, date.plus(1, DateTimeUnit.DAY).atStartOfDayIn(zone))
+    if (end <= start) return null
+    val startMin = wallClockMinutes(start, date, zone)
+    val endMin = wallClockEndMinutes(startMin, start, end, date, zone).coerceAtMost(MINUTES_PER_DAY)
     return TimedBlock(draft, startMin, endMin, lane = 0, laneCount = 1)
 }
 
@@ -312,6 +322,53 @@ enum class ResizeEdge { Top, Bottom }
 /** Where a finished resize asks its event to begin and end. */
 data class TimelineResizeDrop(val event: EventInstance, val start: Instant, val end: Instant)
 
+/**
+ * [event] resized by its [edge] to the span [startMin]..+[spanMin] from [date]'s
+ * midnight. Only the held edge moves. The other keeps its own instant rather than
+ * a round trip through the grid, where an end in the fall-back hour's repeat is
+ * drawn to that hour's end, not at its own time (#387). In a repeated hour, the
+ * held edge takes the pass that matches the direction it was dragged from where
+ * it was drawn (see [repicked]). An end takes a pass the grid draws at the drop
+ * point, so the block settles under the finger.
+ */
+internal fun resizedDrop(
+    event: EventInstance,
+    edge: ResizeEdge?,
+    date: LocalDate,
+    startMin: Int,
+    spanMin: Int,
+    zone: TimeZone,
+): TimelineResizeDrop {
+    val drawn = wallClockSpan(event, zone)
+    return TimelineResizeDrop(
+        event = event,
+        start = if (edge == ResizeEdge.Top) {
+            event.start.toFormTime(zone).repicked(
+                wallClockTime(date, startMin),
+                zone,
+                shownAt = wallClockTime(drawn.day, drawn.startMin),
+                notAfter = event.end,
+            ).instantIn(zone)
+        } else {
+            event.start
+        },
+        end = if (edge == ResizeEdge.Bottom) {
+            val picked = wallClockTime(date, startMin + spanMin)
+            val pickedMin = (picked.date.toEpochDays() - drawn.day.toEpochDays()).toInt() * MINUTES_PER_DAY +
+                picked.time.toSecondOfDay() / 60
+            event.end.toFormTime(zone).repicked(
+                picked,
+                zone,
+                shownAt = wallClockTime(drawn.day, drawn.endMin),
+                notBefore = event.start,
+                drawable = { wallClockEndMinutes(drawn.startMin, event.start, it, drawn.day, zone) == pickedMin },
+            ).instantIn(zone)
+        } else {
+            event.end
+        },
+    )
+}
+
 /**
  * The span after dragging [edge] to [edgeMin] in day [edgeDay], in minutes from the
  * start day's midnight. Snapped, and at least one snap step long.
@@ -547,6 +604,10 @@ class TimelineDragController {
      * finger is on; this is what turns where it lands back into an event start.
      */
     private var clipOffsetMin = 0
+    private var dragZone: TimeZone? = null
+    private var dragDuration = Duration.ZERO
+    /** The dragged event's pass of a repeated hour, worked out once per drag (#387). */
+    private var dragKept: UtcOffset? = null
 
     /** What the picked-up block drew its title over — see [TimelineDrag.titleLines]. */
     private var titleLines = 0
@@ -580,6 +641,7 @@ class TimelineDragController {
     fun begin(
         block: TimedBlock,
         clipOffsetMin: Int,
+        zone: TimeZone,
         titleLines: Int,
         pointerInRoot: Offset,
         blockInRoot: Offset,
@@ -588,6 +650,9 @@ class TimelineDragController {
         if (!isSelected(block)) deselect()
         source = block
         this.clipOffsetMin = clipOffsetMin
+        dragZone = zone
+        dragDuration = (block.event.end - block.event.start).coerceAtLeast(Duration.ZERO)
+        dragKept = zone.repeatedHourOffsetAt(block.event.start)
         this.titleLines = titleLines
         settling = null
         isDragging = true
@@ -605,10 +670,10 @@ class TimelineDragController {
      * Draft a block on an empty slot and lift it at once (#153). It is selected
      * from the start, so it keeps its handles and bar once the finger lets go.
      */
-    fun beginDraft(block: TimedBlock, pointerInRoot: Offset, blockInRoot: Offset) {
+    fun beginDraft(block: TimedBlock, zone: TimeZone, pointerInRoot: Offset, blockInRoot: Offset) {
         deselect()
         select(block.event)
-        begin(block, clipOffsetMin = 0, titleLines = 1, pointerInRoot = pointerInRoot, blockInRoot = blockInRoot)
+        begin(block, clipOffsetMin = 0, zone, titleLines = 1, pointerInRoot = pointerInRoot, blockInRoot = blockInRoot)
     }
 
     fun move(pointerInRoot: Offset) {
@@ -624,6 +689,9 @@ class TimelineDragController {
         resizeSlot = null
         source = null
         clipOffsetMin = 0
+        dragZone = null
+        dragDuration = Duration.ZERO
+        dragKept = null
         titleLines = 0
         isDragging = false
         pointerMoved = false
@@ -748,13 +816,10 @@ class TimelineDragController {
     fun finishResize(zone: TimeZone): TimelineResizeDrop? {
         val landed = drag
         val origin = originSlot
+        val edge = resizeEdge
         cancel()
         if (landed == null || landed.slot == origin) return null
-        val drop = TimelineResizeDrop(
-            event = landed.event,
-            start = wallClockInstant(landed.date, landed.eventStartMin, zone),
-            end = wallClockInstant(landed.date, landed.eventStartMin + landed.eventSpanMin, zone),
-        )
+        val drop = resizedDrop(landed.event, edge, landed.date, landed.eventStartMin, landed.eventSpanMin, zone)
         settlingSelected = selection?.event?.instanceId == landed.event.instanceId
         settling = if (landed.edgeOnly) landed.copy(pieces = emptyList()) else landed
         liftedInstanceId = landed.event.instanceId
@@ -882,13 +947,22 @@ class TimelineDragController {
         val origin = grid.positionInRoot()
         val rawMinutes = (pointer.y - grab.y - origin.y) / hourPx * 60f
         val snapped = (rawMinutes / DRAG_SNAP_MINUTES).roundToInt() * DRAG_SNAP_MINUTES
-        val eventSpan = (block.event.end - block.event.start).inWholeMinutes.toInt()
-            .coerceAtLeast(0)
-        val floor = dragFloorMin(clipOffsetMin, eventSpan)
-        val startMin = snapped.coerceIn(floor, MINUTES_PER_DAY - DRAG_SNAP_MINUTES)
-        val eventStartMin = startMin - clipOffsetMin
+        val zone = dragZone ?: return
         val column = ((pointer.x - origin.x) / columnPx).toInt().coerceIn(0, days.lastIndex)
         val dayIndex = if (geometry.isRtl) days.lastIndex - column else column
+        val target = days[dayIndex]
+        val keep = dragKept
+        // Measured where it would land: the drop keeps the real duration, which in
+        // wall clock gains or loses the hour of a DST change it crosses (#387).
+        val floor = dragFloorMin(
+            clipOffsetMin,
+            wallClockSpanMinutes(target, snapped - clipOffsetMin, dragDuration, zone, keep),
+        )
+        val held = snapped.coerceIn(floor, MINUTES_PER_DAY - DRAG_SNAP_MINUTES) - clipOffsetMin
+        // A start in the spring-forward gap lands an hour on; show it there.
+        val eventStartMin = wallClockInstant(target, held, zone, keep).minutesPast(target, zone)
+        val startMin = (eventStartMin + clipOffsetMin).coerceAtMost(MINUTES_PER_DAY - DRAG_SNAP_MINUTES)
+        val eventSpan = wallClockSpanMinutes(target, eventStartMin, dragDuration, zone, keep)
         val visible = -dayIndex..days.lastIndex - dayIndex
         val onGrid = dragSlices(eventStartMin, eventSpan, within = visible)
         val slices = onGrid.ifEmpty {
@@ -976,10 +1050,7 @@ fun rememberTimelineDragController(): TimelineDragController {
  * so the offset has to come back off at the drop (#253).
  */
 fun TimedBlock.clipOffsetMinutes(day: LocalDate, zone: TimeZone): Int {
-    val start = event.start.toLocalDateTime(zone)
-    val days = (day.toEpochDays() - start.date.toEpochDays()).toInt()
-    val minutes = days * MINUTES_PER_DAY + startMin - start.time.toSecondOfDay() / 60
-    return minutes.coerceAtLeast(0)
+    return (startMin - event.start.minutesPast(day, zone)).coerceAtLeast(0)
 }
 
 /**
@@ -1001,11 +1072,34 @@ fun TimedBlock.continuesAfter(day: LocalDate, zone: TimeZone): Boolean =
  * visibly settles there.
  */
 fun TimelineDrop.startInstant(zone: TimeZone): Instant =
-    wallClockInstant(date, startMin - clipOffsetMin, zone)
+    wallClockInstant(date, startMin - clipOffsetMin, zone, kept = zone.repeatedHourOffsetAt(event.start))
 
-/** [minutes] past [date]'s midnight, either way past it, as wall clock in [zone] (DST-safe). */
-fun wallClockInstant(date: LocalDate, minutes: Int, zone: TimeZone): Instant =
-    wallClockTime(date, minutes).toInstant(zone)
+/**
+ * The wall-clock minutes an event lasting [duration] covers when it starts
+ * [startMin] past [date]'s midnight in [zone] — its real length, give or take a
+ * DST change in between (#387).
+ */
+internal fun wallClockSpanMinutes(
+    date: LocalDate,
+    startMin: Int,
+    duration: Duration,
+    zone: TimeZone,
+    kept: UtcOffset? = null,
+): Int {
+    val start = wallClockInstant(date, startMin, zone, kept)
+    return wallClockEndMinutes(startMin, start, start + duration, date, zone) - startMin
+}
+
+/**
+ * [minutes] past [date]'s midnight, either way past it, as wall clock in [zone]
+ * (DST-safe). A time the fall-back hour repeats lands on its earlier pass, unless
+ * [kept] is its later one: an event there stays on it (#387). Pass
+ * [repeatedHourOffsetAt] of the event's time, which is null outside the hour —
+ * such an instant says nothing about which pass the grid slot means, so a drop
+ * never depends on the season the event came from.
+ */
+fun wallClockInstant(date: LocalDate, minutes: Int, zone: TimeZone, kept: UtcOffset? = null): Instant =
+    wallClockTime(date, minutes).resolveIn(zone, kept)
 
 /** The wall-clock time [minutes] past [date]'s midnight, on a later day past 1440. */
 fun wallClockTime(date: LocalDate, minutes: Int): LocalDateTime {
@@ -1017,14 +1111,18 @@ fun wallClockTime(date: LocalDate, minutes: Int): LocalDateTime {
 /** An event's span as wall-clock minutes from its start day's midnight. */
 data class WallClockSpan(val day: LocalDate, val startMin: Int, val endMin: Int)
 
-/** [event]'s [WallClockSpan], its end past 1440 when it ends on a later day (DST-safe). */
+/**
+ * [event]'s [WallClockSpan], its end past 1440 when it ends on a later day
+ * (DST-safe). One ending in the fall-back hour's repeat ends where that hour does.
+ */
 fun wallClockSpan(event: EventInstance, zone: TimeZone): WallClockSpan {
     val start = event.start.toLocalDateTime(zone)
-    val end = event.end.toLocalDateTime(zone)
     val startMin = start.time.toSecondOfDay() / 60
-    val endMin = (end.date.toEpochDays() - start.date.toEpochDays()).toInt() * MINUTES_PER_DAY +
-        end.time.toSecondOfDay() / 60
-    return WallClockSpan(start.date, startMin, maxOf(startMin, endMin))
+    return WallClockSpan(
+        start.date,
+        startMin,
+        wallClockEndMinutes(startMin, event.start, event.end, start.date, zone),
+    )
 }
 
 /**

app/src/main/java/de/jeanlucmakiola/calendula/ui/detail/EventDetailScreen.kt

@@ -102,6 +102,7 @@ import de.jeanlucmakiola.calendula.ui.common.eventFill
 import de.jeanlucmakiola.floret.locale.currentLocale
 import de.jeanlucmakiola.calendula.ui.common.LocalUse24HourFormat
 import de.jeanlucmakiola.calendula.ui.common.timeOfDayFormatter
+import de.jeanlucmakiola.calendula.ui.common.withRepeatedHourZone
 import de.jeanlucmakiola.calendula.ui.common.recurrenceText
 import de.jeanlucmakiola.calendula.ui.common.reminderLeadTimeLabel
 import kotlinx.coroutines.launch
@@ -377,7 +378,7 @@ private fun EventDetailContent(
         val gap = 12.dp
 
         // "When" — date/all-day plus the time range.
-        val (whenPrimary, whenSecondary) = formatWhen(instance, TimeZone.currentSystemDefault(), locale)
+        val (whenPrimary, whenSecondary) = rememberWhen(instance, TimeZone.currentSystemDefault(), locale)
         DetailCard(icon = Icons.Default.Schedule, iconContentDescription = null) {
             Text(text = whenPrimary, style = MaterialTheme.typography.titleMedium)
             if (whenSecondary != null) {
@@ -417,7 +418,7 @@ private fun EventDetailContent(
                 // in the primary instead, so fall back to it. If the zone can't be
                 // read back at all, drop to just the abbreviation + offset.
                 val originalTime = runCatching { TimeZone.of(zoneOption.id) }.getOrNull()
-                    ?.let { formatWhen(instance, it, locale) }
+                    ?.let { rememberWhen(instance, it, locale) }
                     ?.let { (primary, secondary) -> secondary ?: primary }
                 Spacer(Modifier.height(2.dp))
                 Text(
@@ -806,18 +807,28 @@ private fun linkify(
  * single primary line spanning both ends.
  */
 @Composable
+private fun rememberWhen(instance: EventInstance, zone: TimeZone, locale: Locale): Pair<String, String?> {
+    val use24Hour = LocalUse24HourFormat.current
+    val allDayLabel = stringResource(R.string.event_detail_all_day)
+    // Remembered: a time in the repeated hour looks up its zone abbreviation (#387).
+    return remember(instance, zone, locale, use24Hour, allDayLabel) {
+        formatWhen(instance, zone, locale, use24Hour, allDayLabel)
+    }
+}
+
 private fun formatWhen(
     instance: EventInstance,
     zone: TimeZone,
     locale: Locale,
+    use24Hour: Boolean,
+    allDayLabel: String,
 ): Pair<String, String?> {
     val zid = ZoneId.of(zone.id)
     val dateFull = DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL).withLocale(locale)
     val dateMedium = DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(locale)
-    val timeShort = timeOfDayFormatter(LocalUse24HourFormat.current, locale)
+    val timeShort = timeOfDayFormatter(use24Hour, locale)
 
     val startLdt = instance.start.toJavaLocalDateTime(zid)
-    val allDayLabel = stringResource(R.string.event_detail_all_day)
 
     if (instance.isAllDay) {
         // All-day events live at UTC midnights with an exclusive end. Resolve
@@ -837,12 +848,13 @@ private fun formatWhen(
     }
 
     val endLdt = instance.end.toJavaLocalDateTime(zid)
+    val startTime = withRepeatedHourZone(timeShort.format(startLdt), instance.start, zone, locale)
+    val endTime = withRepeatedHourZone(timeShort.format(endLdt), instance.end, zone, locale)
     return if (startLdt.toLocalDate() == endLdt.toLocalDate()) {
-        dateFull.format(startLdt.toLocalDate()) to
-            "${timeShort.format(startLdt)} – ${timeShort.format(endLdt)}"
+        dateFull.format(startLdt.toLocalDate()) to "$startTime – $endTime"
     } else {
-        val start = "${dateMedium.format(startLdt.toLocalDate())} ${timeShort.format(startLdt)}"
-        val end = "${dateMedium.format(endLdt.toLocalDate())} ${timeShort.format(endLdt)}"
+        val start = "${dateMedium.format(startLdt.toLocalDate())} $startTime"
+        val end = "${dateMedium.format(endLdt.toLocalDate())} $endTime"
         "$start – $end" to null
     }
 }

app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditScreen.kt

@@ -125,10 +125,13 @@ import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventAttendee
 import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventForm
+import de.jeanlucmakiola.calendula.domain.startInstant
+import de.jeanlucmakiola.calendula.domain.endInstant
+import de.jeanlucmakiola.calendula.domain.resolvedZone
+import de.jeanlucmakiola.calendula.domain.isPinnedAwayFrom
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.zoneDescriptor
 import de.jeanlucmakiola.calendula.domain.timeZoneOptionOf
-import de.jeanlucmakiola.calendula.domain.timesIn
 import de.jeanlucmakiola.calendula.domain.EventFormProblem
 import de.jeanlucmakiola.calendula.domain.RecurrenceEnd
 import de.jeanlucmakiola.calendula.domain.RecurrenceFreq
@@ -171,6 +174,7 @@ import de.jeanlucmakiola.floret.reminders.ReminderUnit
 import de.jeanlucmakiola.floret.locale.currentLocale
 import de.jeanlucmakiola.calendula.ui.common.LocalUse24HourFormat
 import de.jeanlucmakiola.calendula.ui.common.timeOfDayFormatter
+import de.jeanlucmakiola.calendula.ui.common.withRepeatedHourZone
 import de.jeanlucmakiola.calendula.ui.common.reminderLeadTimeLabel
 import de.jeanlucmakiola.calendula.ui.common.reminderUnitLabel
 import de.jeanlucmakiola.calendula.ui.common.nextOccurrencesText
@@ -183,7 +187,6 @@ import kotlinx.datetime.TimeZone
 import kotlinx.datetime.isoDayNumber
 import kotlinx.datetime.toJavaDayOfWeek
 import kotlinx.datetime.toJavaLocalDate
-import kotlinx.datetime.toInstant
 import kotlinx.datetime.toJavaLocalTime
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.toJavaInstant
@@ -193,6 +196,7 @@ import java.time.format.FormatStyle
 import java.time.format.TextStyle as JavaTextStyle
 import java.util.Locale
 import kotlin.time.Clock
+import kotlin.time.Instant
 
 /**
  * Full-screen event form: create (v1.2, from the FAB's anchor date) and edit
@@ -214,7 +218,7 @@ fun EventEditScreen(
     onSaved: () -> Unit,
     editKey: LongArray? = null,
     initialStartMinutes: Int? = null,
-    initialEndMinutes: Int? = null,
+    initialDraft: LongArray? = null,
     initialForm: EventForm? = null,
     initialFormSource: ImportSource = ImportSource.File,
     onManageCalendars: (() -> Unit)? = null,
@@ -224,7 +228,9 @@ fun EventEditScreen(
     visible: Boolean = true,
     viewModel: EventEditViewModel = hiltViewModel(),
 ) {
-    LaunchedEffect(initialDateIso, editKey, initialForm) {
+    // Keyed on every input that decides the form, so a second draft or slot on
+    // the same day opens its own form even when the composition is kept alive.
+    LaunchedEffect(initialDateIso, editKey, initialForm, initialDraft, initialStartMinutes) {
         when {
             // A prefilled open: a single-event .ics for review, or an external
             // ACTION_INSERT intent. The source drives how reminders are seeded.
@@ -234,10 +240,15 @@ fun EventEditScreen(
                 beginMillis = editKey[1],
                 endMillis = editKey[2],
             )
+            // A block drafted on the timeline (#153): its own start and end.
+            initialDraft != null -> viewModel.openDraft(
+                start = Instant.fromEpochMilliseconds(initialDraft[0]),
+                end = Instant.fromEpochMilliseconds(initialDraft[1]),
+            )
             else -> {
                 val date = initialDateIso?.let { runCatching { LocalDate.parse(it) }.getOrNull() }
-                    ?: Clock.System.now().toLocalDateTime(TimeZone.currentSystemDefault()).date
-                viewModel.openNew(date, initialStartMinutes, initialEndMinutes)
+                    ?: Clock.System.now().toLocalDateTime(viewModel.zone.value).date
+                viewModel.openNew(date, initialStartMinutes)
             }
         }
     }
@@ -681,6 +692,7 @@ private fun EventEditContent(
 ) {
     val form = state.form
     val locale = currentLocale()
+    val deviceZone by viewModel.zone.collectAsStateWithLifecycle()
     val firstDayOfWeek by viewModel.firstDayOfWeek.collectAsStateWithLifecycle()
     val dark = isSystemInDarkTheme()
     // The title, date and recurrence are managed by the special-dates sync, so
@@ -842,9 +854,14 @@ private fun EventEditContent(
             },
         ) {
             Spacer(Modifier.height(4.dp))
+            val formZone = remember(form.timezone, deviceZone) { form.resolvedZone(deviceZone) }
+            val startAt = remember(form.start, formZone) { form.startInstant(formZone) }
+            val endAt = remember(form.end, formZone) { form.endInstant(formZone) }
             ScheduleRow(
                 label = stringResource(R.string.event_edit_starts),
-                dateTime = form.start,
+                dateTime = form.start.dateTime,
+                instant = startAt,
+                zone = formZone,
                 isAllDay = form.isAllDay,
                 locale = locale,
                 onDateClick = { picker = PickerTarget.StartDate },
@@ -853,7 +870,9 @@ private fun EventEditContent(
             )
             ScheduleRow(
                 label = stringResource(R.string.event_edit_ends),
-                dateTime = form.end,
+                dateTime = form.end.dateTime,
+                instant = endAt,
+                zone = formZone,
                 isAllDay = form.isAllDay,
                 locale = locale,
                 onDateClick = { picker = PickerTarget.EndDate },
@@ -872,20 +891,20 @@ private fun EventEditContent(
             // The rows above edit a pinned event in *its own* zone, which is the
             // time it was set at — but that says nothing about when it lands for
             // whoever is reading it. Spell the local equivalent out rather than
-            // leaving the user to do the offset arithmetic. Absent (null) unless
-            // the event is pinned somewhere other than here.
+            // leaving the user to do the offset arithmetic. Absent unless the
+            // event is pinned somewhere other than here.
             // Keyed rather than recomputed: this sits in the same Column as the
             // title field, so it would otherwise re-parse the zone on every
             // keystroke.
-            val localTimes = remember(form.timezone, form.start, form.end, form.isAllDay) {
-                form.timesIn(TimeZone.currentSystemDefault())
+            val pinnedAway = remember(form.timezone, form.isAllDay, deviceZone) {
+                form.isPinnedAwayFrom(deviceZone)
             }
-            localTimes?.let { (localStart, localEnd) ->
+            if (pinnedAway) {
                 Spacer(Modifier.height(2.dp))
                 Text(
                     text = stringResource(
                         R.string.event_edit_timezone_local_time,
-                        formatTimeRange(localStart, localEnd, locale),
+                        formatTimeRange(startAt, endAt, deviceZone, locale),
                     ),
                     style = MaterialTheme.typography.bodySmall,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
@@ -949,7 +968,7 @@ private fun EventEditContent(
                                 timeZoneOptionOf(
                                     id,
                                     locale,
-                                    at = form.start.toInstant(zone).toJavaInstant(),
+                                    at = form.startInstant(zone).toJavaInstant(),
                                     regionOf = ::icuTimeZoneRegion,
                                 )
                             }
@@ -2431,18 +2450,23 @@ private fun EditCard(
 }
 
 /**
- * "2:00 PM – 3:00 PM", honouring the user's 12/24-hour setting. Collapses to one
- * time when both land on the same minute (an instant event shouldn't read as a
- * range against itself). Dates are deliberately absent — the rows above carry
- * them.
+ * "2:00 PM – 3:00 PM" in [zone], honouring the user's 12/24-hour setting. Collapses
+ * to one time for an instant event, which shouldn't read as a range against
+ * itself. Dates are deliberately absent — the rows above carry them.
  */
 @Composable
-private fun formatTimeRange(start: LocalDateTime, end: LocalDateTime, locale: Locale): String {
+private fun formatTimeRange(start: Instant, end: Instant, zone: TimeZone, locale: Locale): String {
     val use24Hour = LocalUse24HourFormat.current
-    val timeFormat = remember(locale, use24Hour) { timeOfDayFormatter(use24Hour, locale) }
-    val from = timeFormat.format(start.time.toJavaLocalTime())
-    val to = timeFormat.format(end.time.toJavaLocalTime())
-    return if (from == to) from else "$from – $to"
+    return remember(start, end, zone, locale, use24Hour) {
+        val timeFormat = timeOfDayFormatter(use24Hour, locale)
+        fun format(at: Instant) = withRepeatedHourZone(
+            timeFormat.format(at.toLocalDateTime(zone).time.toJavaLocalTime()),
+            at,
+            zone,
+            locale,
+        )
+        if (start == end) format(start) else "${format(start)} – ${format(end)}"
+    }
 }
 
 /**
@@ -2524,6 +2548,8 @@ private fun firstLineHeight(
 private fun ScheduleRow(
     label: String,
     dateTime: LocalDateTime,
+    instant: Instant,
+    zone: TimeZone,
     isAllDay: Boolean,
     locale: Locale,
     onDateClick: () -> Unit,
@@ -2565,8 +2591,11 @@ private fun ScheduleRow(
                 .padding(vertical = 8.dp, horizontal = 6.dp),
         )
         if (!isAllDay) {
+            val time = remember(dateTime, instant, zone, locale, timeFormat) {
+                withRepeatedHourZone(timeFormat.format(dateTime.time.toJavaLocalTime()), instant, zone, locale)
+            }
             Text(
-                text = timeFormat.format(dateTime.time.toJavaLocalTime()),
+                text = time,
                 style = MaterialTheme.typography.titleMedium,
                 color = valueColor,
                 modifier = Modifier

app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt

@@ -11,6 +11,7 @@ import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.ics.IcsExporter
 import de.jeanlucmakiola.calendula.data.prefs.CalendarPrefs
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
+import de.jeanlucmakiola.calendula.data.time.ZoneSource
 import de.jeanlucmakiola.calendula.data.prefs.firstDayOfWeek
 import de.jeanlucmakiola.calendula.data.prefs.resolveDefaultEventDuration
 import de.jeanlucmakiola.calendula.data.prefs.resolveDefaultReminder
@@ -22,6 +23,15 @@ import de.jeanlucmakiola.calendula.domain.EventAttendee
 import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventDetail
 import de.jeanlucmakiola.calendula.domain.EventForm
+import de.jeanlucmakiola.calendula.domain.endInstant
+import de.jeanlucmakiola.calendula.domain.nextFullHour
+import de.jeanlucmakiola.calendula.domain.toFormTime
+import de.jeanlucmakiola.calendula.domain.resolvedZone
+import de.jeanlucmakiola.calendula.domain.startInstant
+import de.jeanlucmakiola.calendula.domain.withEnd
+import de.jeanlucmakiola.calendula.domain.withStart
+import de.jeanlucmakiola.calendula.domain.withTimes
+import de.jeanlucmakiola.calendula.domain.withTimezone
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.RecurringWriteScope
 import de.jeanlucmakiola.calendula.domain.isEventTarget
@@ -32,7 +42,6 @@ import de.jeanlucmakiola.calendula.ui.detail.EventDetailViewModel.Companion.NO_O
 import de.jeanlucmakiola.calendula.ui.common.DeleteOutcome
 import de.jeanlucmakiola.calendula.ui.common.tryDeleteEvent
 import de.jeanlucmakiola.calendula.ui.common.stageEventShare
-import de.jeanlucmakiola.calendula.ui.common.wallClockTime
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
@@ -141,8 +150,13 @@ class EventEditViewModel @Inject constructor(
     private val settingsPrefs: SettingsPrefs,
     private val icsExporter: IcsExporter,
     @IoDispatcher private val io: CoroutineDispatcher,
+    private val zoneSource: ZoneSource,
 ) : ViewModel() {
 
+    /** The zone the form's unpinned times are read in, for the screen to show them in too. */
+    val zone: StateFlow<TimeZone> = zoneSource.zone
+        .stateIn(viewModelScope, SharingStarted.Eagerly, zoneSource.current())
+
     private val _form = MutableStateFlow<EventForm?>(null)
     private val _saveState = MutableStateFlow<SaveUiState>(SaveUiState.Idle)
     // Problems stay hidden until the first save attempt, so a half-filled
@@ -302,7 +316,11 @@ class EventEditViewModel @Inject constructor(
         EventEditUiState(
             form = resolved,
             calendars = pickerCalendars,
-            problems = if (local.showProblems) resolved.problems() else emptySet(),
+            problems = if (local.showProblems) {
+                resolved.problems(zoneSource.current())
+            } else {
+                emptySet()
+            },
             saveState = local.saveState,
             visibleFields = visibleFields,
             hiddenFields = (offerableFields - visibleFields).sorted(),
@@ -349,32 +367,37 @@ class EventEditViewModel @Inject constructor(
      * in the day/week grid; without it the default is the next full hour (today)
      * or 09:00 (any other day). The event opens an hour long and is stretched to
      * the configured default by [applyDefaultDuration], like the reminders.
-     * A block drafted on the timeline (#153) passes [endMinutes] instead,
-     * counted from [date]'s midnight and past 1440 for a later day.
      * No-op when a form is already open, so user input survives configuration
      * changes; [reset] clears it when the screen closes.
      */
-    fun openNew(date: LocalDate, startMinutes: Int? = null, endMinutes: Int? = null) {
+    fun openNew(date: LocalDate, startMinutes: Int? = null) {
         if (_form.value != null) return
-        val zone = TimeZone.currentSystemDefault()
+        val zone = zoneSource.current()
         val now = Clock.System.now()
-        val start = when {
+        val startAt = when {
             startMinutes != null ->
-                LocalDateTime(date, LocalTime(startMinutes / 60, startMinutes % 60))
-            date == now.toLocalDateTime(zone).date -> {
-                // Today: the next full hour (may roll into tomorrow before midnight).
-                val hourMillis = 3_600_000L
-                val rounded = (now.toEpochMilliseconds() / hourMillis + 1) * hourMillis
-                Instant.fromEpochMilliseconds(rounded).toLocalDateTime(zone)
-            }
-            else -> LocalDateTime(date, LocalTime(9, 0))
+                LocalDateTime(date, LocalTime(startMinutes / 60, startMinutes % 60)).toInstant(zone)
+            date == now.toLocalDateTime(zone).date -> nextFullHour(now)
+            else -> LocalDateTime(date, LocalTime(9, 0)).toInstant(zone)
         }
-        val chosenEnd = endMinutes?.takeIf { startMinutes != null && it > startMinutes }
-            ?.let { wallClockTime(date, it) }
-        val end = chosenEnd ?: (start.toInstant(zone) + SettingsPrefs.DEFAULT_EVENT_DURATION.minutes)
-            .toLocalDateTime(zone)
-        _form.value = EventForm(calendarId = null, start = start, end = end)
-        if (chosenEnd != null) _durationTouched.value = true
+        val endAt = startAt + SettingsPrefs.DEFAULT_EVENT_DURATION.minutes
+        _form.value = EventForm(calendarId = null, start = startAt.toFormTime(zone), end = endAt.toFormTime(zone))
+        applyDefaultReminder()
+        applyDefaultDuration()
+    }
+
+    /**
+     * Initialise a fresh form for a block drafted on the timeline (#153), from
+     * [start] to [end]. These are the instants the block shows, so a time in the
+     * fall-back hour's repeat, or one moved out of the spring-forward gap, opens
+     * as drawn (#387). The user chose the length, so the default length doesn't
+     * apply. No-op when a form is already open, as [openNew].
+     */
+    fun openDraft(start: Instant, end: Instant) {
+        if (_form.value != null) return
+        val zone = zoneSource.current()
+        _form.value = EventForm(calendarId = null, start = start.toFormTime(zone), end = end.toFormTime(zone))
+        _durationTouched.value = true
         applyDefaultReminder()
         applyDefaultDuration()
     }
@@ -484,11 +507,10 @@ class EventEditViewModel @Inject constructor(
             if (_editTarget.value != null || _durationTouched.value) return@launch
             if (_form.value?.isAllDay != false) return@launch
             val duration = resolveDefaultEventDuration(global, overrides, targetId)
-            val zone = TimeZone.currentSystemDefault()
             update { form ->
-                form.copy(
-                    end = (form.start.toInstant(zone) + duration.minutes).toLocalDateTime(zone),
-                )
+                val zone = form.resolvedZone(zoneSource.current())
+                val start = form.startInstant(zone)
+                form.withTimes(start, start + duration.minutes, zone)
             }
         }
     }
@@ -549,7 +571,7 @@ class EventEditViewModel @Inject constructor(
                 _loadFailed.value = true
                 return@launch
             }
-            val zone = TimeZone.currentSystemDefault()
+            val zone = zoneSource.current()
             val begin = beginMillis.takeUnless { it == NO_OCCURRENCE_TIME }
                 ?: detail.instance.start.toEpochMilliseconds()
             val end = endMillis.takeUnless { it == NO_OCCURRENCE_TIME }
@@ -607,7 +629,11 @@ class EventEditViewModel @Inject constructor(
         // the provider stores UTC-anchored, so a zone could only misrepresent
         // them. Coming back out of all-day leaves the event on the device zone,
         // which is the same thing a fresh event gets.
-        edit { it.copy(isAllDay = value, timezone = if (value) null else it.timezone) }
+        // A kept pass of a repeated hour stays, so switching back out of all-day
+        // lands where the event was — unless dropping the pin changed the zone.
+        edit {
+            if (value) it.withTimezone(null, zoneSource.current()).copy(isAllDay = true) else it.copy(isAllDay = false)
+        }
         // The default reminder differs for all-day vs timed; re-apply the
         // type-appropriate default unless the user has hand-edited it (guarded).
         applyDefaultReminder()
@@ -622,7 +648,7 @@ class EventEditViewModel @Inject constructor(
      * time — only real picks are remembered, not the device fallback.
      */
     fun setTimezone(zoneId: String?) {
-        edit { it.copy(timezone = zoneId) }
+        edit { it.withTimezone(zoneId, zoneSource.current()) }
         if (zoneId != null) {
             viewModelScope.launch { withContext(io) { settingsPrefs.addRecentTimeZone(zoneId) } }
         }
@@ -700,12 +726,12 @@ class EventEditViewModel @Inject constructor(
     // default duration, so a later calendar switch keeps their span (#54).
     fun setEndDate(date: LocalDate) {
         _durationTouched.value = true
-        edit { it.copy(end = LocalDateTime(date, it.end.time)) }
+        moveEnd { LocalDateTime(date, it.time) }
     }
 
     fun setEndTime(time: LocalTime) {
         _durationTouched.value = true
-        edit { it.copy(end = LocalDateTime(it.end.date, time)) }
+        moveEnd { LocalDateTime(it.date, time) }
     }
 
     /**
@@ -718,7 +744,7 @@ class EventEditViewModel @Inject constructor(
         val current = state.value ?: return
         if (current.saveState == SaveUiState.Saving) return
         val form = current.form
-        if (form.problems().isNotEmpty()) {
+        if (form.problems(zoneSource.current()).isNotEmpty()) {
             _showProblems.value = true
             return
         }
@@ -874,13 +900,20 @@ class EventEditViewModel @Inject constructor(
     }
 
     private fun moveStart(transform: (LocalDateTime) -> LocalDateTime) = edit { form ->
-        val zone = TimeZone.currentSystemDefault()
-        val newStart = transform(form.start)
-        val duration = form.end.toInstant(zone) - form.start.toInstant(zone)
-        val newEnd = (newStart.toInstant(zone) + duration).toLocalDateTime(zone)
-        form.copy(start = newStart, end = newEnd)
+        form.withStart(transform(form.start.dateTime), form.resolvedZone(zoneSource.current()), opened(form)?.start)
     }
 
+    private fun moveEnd(transform: (LocalDateTime) -> LocalDateTime) = edit { form ->
+        form.withEnd(transform(form.end.dateTime), form.resolvedZone(zoneSource.current()), opened(form)?.end)
+    }
+
+    /**
+     * The event as it was opened, while its times still mean the same instants:
+     * picking one of them again keeps its pass of a repeated hour (#387).
+     */
+    private fun opened(form: EventForm): EventForm? =
+        _editTarget.value?.original?.takeIf { it.timezone == form.timezone && !it.isAllDay }
+
     private inline fun update(block: (EventForm) -> EventForm) {
         _form.value = _form.value?.let(block)
     }

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekScreen.kt

@@ -52,6 +52,7 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.staticCompositionLocalOf
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.key
@@ -73,7 +74,6 @@ import de.jeanlucmakiola.calendula.ui.common.rememberDragSurface
 import de.jeanlucmakiola.calendula.ui.common.rememberWriteGate
 import de.jeanlucmakiola.calendula.ui.common.OutOfViewEdges
 import de.jeanlucmakiola.calendula.ui.common.wallClockInstant
-import de.jeanlucmakiola.calendula.ui.common.wallClockSpan
 import de.jeanlucmakiola.calendula.ui.common.PickUp
 import de.jeanlucmakiola.calendula.ui.common.SelectionBarClearance
 import de.jeanlucmakiola.calendula.ui.common.ResizeEdge
@@ -100,6 +100,7 @@ import androidx.compose.runtime.SideEffect
 import de.jeanlucmakiola.calendula.ui.common.laneSlot
 import de.jeanlucmakiola.calendula.ui.common.LaneColumn
 import kotlin.math.roundToInt
+import kotlin.time.Instant
 import androidx.compose.ui.unit.Constraints
 import androidx.compose.ui.layout.Layout
 import androidx.compose.ui.draw.alpha
@@ -249,7 +250,7 @@ fun TimelineScreen(
     onOpenDay: (LocalDate) -> Unit,
     onEventClick: (EventInstance) -> Unit,
     onCreateEvent: (LocalDate, Int?) -> Unit,
-    onCreateSpan: (LocalDate, Int, Int?) -> Unit,
+    onCreateDraft: (Instant, Instant) -> Unit,
     modifier: Modifier = Modifier,
     weekViewModel: WeekViewModel = hiltViewModel(),
     multiDayViewModel: MultiDayViewModel = hiltViewModel(),
@@ -264,7 +265,7 @@ fun TimelineScreen(
         onOpenDay = onOpenDay,
         onEventClick = onEventClick,
         onCreateEvent = onCreateEvent,
-        onCreateSpan = onCreateSpan,
+        onCreateDraft = onCreateDraft,
         modifier = modifier,
     )
 }
@@ -311,6 +312,12 @@ internal val CalendarView.timelineKind: TimelineKind
         else -> TimelineKind.Week
     }
 
+/**
+ * The zone the shown timeline is laid out in, so its blocks, drags and drops all
+ * read the same wall clock (#387).
+ */
+internal val LocalTimelineZone = staticCompositionLocalOf { TimeZone.currentSystemDefault() }
+
 /** How long a switch waits for the view it goes to before resizing into it without its events. */
 private const val MORPH_DATA_WAIT_MS = 150L
 
@@ -322,7 +329,7 @@ private fun PagedTimelineScreen(
     onOpenDay: (LocalDate) -> Unit,
     onEventClick: (EventInstance) -> Unit,
     onCreateEvent: (LocalDate, Int?) -> Unit,
-    onCreateSpan: (LocalDate, Int, Int?) -> Unit,
+    onCreateDraft: (Instant, Instant) -> Unit,
     modifier: Modifier,
 ) {
     // The view on screen, which trails [view] while the columns resize into it.
@@ -449,7 +456,8 @@ private fun PagedTimelineScreen(
 
     // Off the ticking clock rather than the loaded page, so it turns over at
     // midnight; derived, so the per-minute tick doesn't recompose the screen.
-    val zone = remember { TimeZone.currentSystemDefault() }
+    // The timeline's own zone, so "today" agrees with the blocks and drops (#387).
+    val zone by viewModel.zone.collectAsStateWithLifecycle()
     val today by remember(zone) { derivedStateOf { nowState.value.toLocalDateTime(zone).date } }
     val isOnCurrentWeek = state !is WeekUiState.Success || (today >= weekStart && today <= weekEnd)
 
@@ -490,7 +498,10 @@ private fun PagedTimelineScreen(
     )
 
     ScreenBody(modifier = modifier) { innerPadding ->
-        CompositionLocalProvider(LocalDimCutoff provides dimCutoff) {
+        CompositionLocalProvider(
+            LocalDimCutoff provides dimCutoff,
+            LocalTimelineZone provides zone,
+        ) {
             WeekContent(
                 state = state,
                 today = today,
@@ -504,7 +515,7 @@ private fun PagedTimelineScreen(
                 onEventClick = onEventClick,
                 onOpenDay = onOpenDay,
                 onCreateAt = { d, minutes -> onCreateEvent(d, minutes) },
-                onCreateSpan = onCreateSpan,
+                onCreateDraft = onCreateDraft,
                 draftMinutes = draftMinutes,
                 modifier = Modifier
                     .padding(innerPadding)
@@ -528,7 +539,7 @@ private fun WeekContent(
     onEventClick: (EventInstance) -> Unit,
     onOpenDay: (LocalDate) -> Unit,
     onCreateAt: (LocalDate, Int) -> Unit,
-    onCreateSpan: (LocalDate, Int, Int?) -> Unit,
+    onCreateDraft: (Instant, Instant) -> Unit,
     draftMinutes: Int,
     modifier: Modifier = Modifier,
 ) {
@@ -546,7 +557,7 @@ private fun WeekContent(
     val dragController = rememberTimelineDragController()
     SideEffect { dragController.draftMinutes = draftMinutes }
     val move = LocalEventMove.current
-    val zone = remember { TimeZone.currentSystemDefault() }
+    val zone = LocalTimelineZone.current
     val onDrop: (TimelineDrop) -> Unit = drop@{ drop ->
         val start = drop.startInstant(zone)
         val moved = drop.event.copy(start = start, end = start + (drop.event.end - drop.event.start))
@@ -587,11 +598,11 @@ private fun WeekContent(
         )
     }
 
-    // A drafted block (#153) opens the new-event form at the span it shows.
+    // A drafted block (#153) opens the new-event form at its own instants: the
+    // end it is drawn to differs on a DST change (#387).
     val createDraft: (EventInstance) -> Unit = { draft ->
         dragController.deselect()
-        val span = wallClockSpan(draft, zone)
-        onCreateSpan(span.day, span.startMin, span.endMin)
+        onCreateDraft(draft.start, draft.end)
     }
 
     // Selection (#141) ends on back, a page or view change, or any tap.
@@ -1410,7 +1421,7 @@ private fun DayColumnCard(
     val hourPx = with(density) { hourHeight.toPx() }
     val morphing = LocalViewMorph.current != null
     val showHourGrid = LocalShowHourGrid.current
-    val zone = remember { TimeZone.currentSystemDefault() }
+    val zone = LocalTimelineZone.current
     // A block drafted on an empty slot (#153), drawn over the part of it on this day.
     val draft by remember(dragController) {
         derivedStateOf { dragController.selection?.event?.takeIf { it.isDraft } }
@@ -1576,8 +1587,10 @@ private fun EventBlock(
     val title = block.event.title.ifBlank { stringResource(R.string.event_untitled) }
     val use24Hour = LocalUse24HourFormat.current
     val locale = currentLocale()
+    val zone = LocalTimelineZone.current
+    val labelEndMin = remember(block, date, zone) { block.labelEndMin(date, zone) }
     val timeLabel = "${minToHm(block.startMin, use24Hour, locale)}–" +
-        minToHm(block.endMin, use24Hour, locale)
+        minToHm(labelEndMin, use24Hour, locale)
     val density = LocalDensity.current
     val metrics = rememberBlockTextMetrics(height)
     // Only full-width (non-overlapping) blocks that are tall enough show the
@@ -1591,7 +1604,7 @@ private fun EventBlock(
     val textWidth = width - (BLOCK_OUTER_INSET + BLOCK_TEXT_PADDING) * 2
     val shownTime = rememberBlockTimeRange(
         minToHm(block.startMin, use24Hour, locale),
-        minToHm(block.endMin, use24Hour, locale),
+        minToHm(labelEndMin, use24Hour, locale),
         textWidth,
     )
     // A short block drops the title rather than serving a horizontally sliced
@@ -1622,7 +1635,6 @@ private fun EventBlock(
     val timeMaxLines = if (showTime) blockTimeLines(shownTime, textWidth, spare) else 1
     val dimCutoff = LocalDimCutoff.current
     val dimmed = dimCutoff != null && block.event.isPastOn(date, dimCutoff)
-    val zone = remember { TimeZone.currentSystemDefault() }
     val moveAction = eventMoveAction(block.event)
     val draft = block.event.isDraft
     val draggable = draft || eventDragAllowed(block.event)
@@ -1644,6 +1656,7 @@ private fun EventBlock(
                 dragController.begin(
                     block = block,
                     clipOffsetMin = clipOffset,
+                    zone = zone,
                     titleLines = if (showTitle) titleMaxLines else 0,
                     pointerInRoot = pointer,
                     // Measured off the block's placement rather than off where the
@@ -1806,7 +1819,7 @@ private fun rememberDraftSurface(
     val currentDrop by rememberUpdatedState(onDrop)
     val title = stringResource(R.string.event_edit_new_title)
     val color = MaterialTheme.colorScheme.primary.toArgb()
-    val zone = remember { TimeZone.currentSystemDefault() }
+    val zone = LocalTimelineZone.current
     val currentEdges by rememberUpdatedState(edges)
     // The draft this gesture lifted, selected again on release after the cancel.
     val lifted = remember { arrayOfNulls<EventInstance>(1) }
@@ -1830,6 +1843,7 @@ private fun rememberDraftSurface(
             lifted[0] = event
             dragController.beginDraft(
                 block = block,
+                zone = zone,
                 pointerInRoot = pointer,
                 blockInRoot = node + Offset(0f, startMin / 60f * hour),
             )

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekViewModel.kt

@@ -8,6 +8,7 @@ import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.data.prefs.resolveFirstDay
 import de.jeanlucmakiola.calendula.data.time.TodaySource
+import de.jeanlucmakiola.calendula.data.time.ZoneSource
 import de.jeanlucmakiola.calendula.data.time.currentDate
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventInstance
@@ -34,7 +35,10 @@ import kotlinx.coroutines.flow.stateIn
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.DayOfWeek
 import kotlinx.datetime.LocalDate
+import kotlinx.datetime.FixedOffsetTimeZone
 import kotlinx.datetime.TimeZone
+import kotlinx.datetime.toKotlinUtcOffset
+import kotlinx.datetime.toJavaZoneId
 import kotlinx.datetime.atStartOfDayIn
 import kotlinx.datetime.atTime
 import kotlinx.datetime.daysUntil
@@ -44,6 +48,8 @@ import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
 import java.util.Locale
 import kotlin.time.Instant
+import kotlin.time.toKotlinDuration
+import kotlin.time.toKotlinInstant
 import javax.inject.Inject
 import kotlin.math.abs
 
@@ -76,12 +82,18 @@ abstract class PagedTimelineViewModel(
     private val repository: CalendarRepository,
     settingsPrefs: SettingsPrefs,
     todaySource: TodaySource,
+    zoneSource: ZoneSource,
     private val io: CoroutineDispatcher,
     gridRule: Flow<(LocalDate) -> PageGrid>,
     initialRule: (LocalDate) -> PageGrid,
 ) : ViewModel() {
 
-    private val zone = TimeZone.currentSystemDefault()
+    /**
+     * The zone every page is laid out in; drags and drops resolve in it too, and
+     * pages lay out again when the device moves zones (#387).
+     */
+    val zone: StateFlow<TimeZone> = zoneSource.zone
+        .stateIn(viewModelScope, SharingStarted.Eagerly, zoneSource.current())
 
     /** Whether to fade events that have already finished (display concern only). */
     val dimCompletedEvents: StateFlow<Boolean> = settingsPrefs.dimCompletedEvents
@@ -160,12 +172,14 @@ abstract class PagedTimelineViewModel(
                 abs(cached.start.daysUntil(requested.start)) <= SPAN_CACHE_DAYS
         },
     ) { span ->
-        combine(
-            repository.calendars(),
-            repository.instances(spanRange(span.start, span.count, zone)),
-            today,
-        ) { calendars, instances, today ->
-            buildState(span, calendars, instances, today)
+        zone.flatMapLatest { zone ->
+            combine(
+                repository.calendars(),
+                repository.instances(spanRange(span.start, span.count, zone)),
+                today,
+            ) { calendars, instances, today ->
+                buildState(span, calendars, instances, today, zone)
+            }
         }
             .catch { emit(WeekUiState.Failure(FailureReason.ProviderUnavailable)) }
             .flowOn(io)
@@ -200,6 +214,7 @@ abstract class PagedTimelineViewModel(
         calendars: List<CalendarSource>,
         instances: List<EventInstance>,
         today: LocalDate,
+        zone: TimeZone,
     ): WeekUiState {
         calendarListFailure(calendars)?.let { return WeekUiState.Failure(it) }
         val days = (0 until span.count).map { span.start.plus(it, DateTimeUnit.DAY) }
@@ -221,11 +236,13 @@ class WeekViewModel @Inject constructor(
     repository: CalendarRepository,
     settingsPrefs: SettingsPrefs,
     todaySource: TodaySource,
+    zoneSource: ZoneSource,
     @IoDispatcher io: CoroutineDispatcher,
 ) : PagedTimelineViewModel(
     repository = repository,
     settingsPrefs = settingsPrefs,
     todaySource = todaySource,
+    zoneSource = zoneSource,
     io = io,
     gridRule = settingsPrefs.weekStart.map { pref ->
         val grid = WeekGrid(pref.resolveFirstDay(Locale.getDefault()))
@@ -245,11 +262,13 @@ class MultiDayViewModel @Inject constructor(
     repository: CalendarRepository,
     settingsPrefs: SettingsPrefs,
     todaySource: TodaySource,
+    zoneSource: ZoneSource,
     @IoDispatcher io: CoroutineDispatcher,
 ) : PagedTimelineViewModel(
     repository = repository,
     settingsPrefs = settingsPrefs,
     todaySource = todaySource,
+    zoneSource = zoneSource,
     io = io,
     gridRule = settingsPrefs.multiDayCount.map { count ->
         { anchor: LocalDate -> DaysGrid.startingAt(anchor, count) }
@@ -263,11 +282,13 @@ class DayViewModel @Inject constructor(
     repository: CalendarRepository,
     settingsPrefs: SettingsPrefs,
     todaySource: TodaySource,
+    zoneSource: ZoneSource,
     @IoDispatcher io: CoroutineDispatcher,
 ) : PagedTimelineViewModel(
     repository = repository,
     settingsPrefs = settingsPrefs,
     todaySource = todaySource,
+    zoneSource = zoneSource,
     io = io,
     gridRule = flowOf { _: LocalDate -> DayGrid },
     initialRule = { DayGrid },
@@ -339,6 +360,64 @@ internal fun spanRange(start: LocalDate, count: Int, zone: TimeZone): ClosedRang
     return from..to
 }
 
+/**
+ * This instant's wall-clock time as minutes past [day]'s midnight in [zone] —
+ * negative before that day, past 1440 after it. Elapsed time since midnight would
+ * put everything after a DST change an hour off on that day's grid (#387).
+ */
+internal fun Instant.minutesPast(day: LocalDate, zone: TimeZone): Int {
+    val local = toLocalDateTime(zone)
+    val days = (local.date.toEpochDays() - day.toEpochDays()).toInt()
+    return days * MINUTES_PER_DAY + local.time.toSecondOfDay() / 60
+}
+
+/** [instant]'s [minutesPast] clamped to [day]. */
+internal fun wallClockMinutes(instant: Instant, day: LocalDate, zone: TimeZone): Int =
+    instant.minutesPast(day, zone).coerceIn(0, MINUTES_PER_DAY)
+
+/**
+ * Where a run from [start] to [end] that begins at [startMin] ends on [day]'s
+ * wall clock. A run that began before the fall-back hour's repeat and ends
+ * inside it is drawn to where that hour ends (03:00 in Berlin), since its own
+ * wall-clock end reads earlier than its real length (#387).
+ */
+internal fun wallClockEndMinutes(
+    startMin: Int,
+    start: Instant,
+    end: Instant,
+    day: LocalDate,
+    zone: TimeZone,
+): Int {
+    val wall = end.minutesPast(day, zone)
+    if (end <= start) return maxOf(wall, startMin)
+    val drawn = repeatedHourEndMinutes(start, end, day, zone) ?: wall
+    return if (drawn > startMin) drawn else startMin + (end - start).inWholeMinutes.toInt()
+}
+
+/**
+ * Where the fall-back hour's repeat [end] falls in ends, as minutes past [day]'s
+ * midnight: the wall clock the zone fell back from (03:00 in Berlin). Null unless
+ * [end] is in that repeat and [start] before it.
+ */
+private fun repeatedHourEndMinutes(start: Instant, end: Instant, day: LocalDate, zone: TimeZone): Int? {
+    // Just past [end], so an end on the transition itself still finds it.
+    val after = java.time.Instant.ofEpochMilli(end.toEpochMilliseconds() + 1)
+    val transition = zone.toJavaZoneId().rules.previousTransition(after)
+        ?.takeIf { it.isOverlap } ?: return null
+    val fellBack = transition.instant.toKotlinInstant()
+    if (start >= fellBack || end >= fellBack + transition.duration.abs().toKotlinDuration()) return null
+    // The moment it fell back, read on the clock it fell back from.
+    return fellBack.minutesPast(day, FixedOffsetTimeZone(transition.offsetBefore.toKotlinUtcOffset()))
+}
+
+/**
+ * The end a block's time label names on [day]: its event's own wall-clock end,
+ * which for one ending in the fall-back hour's repeat is earlier than the
+ * [TimedBlock.endMin] it is drawn to (#387).
+ */
+internal fun TimedBlock.labelEndMin(day: LocalDate, zone: TimeZone): Int =
+    minOf(endMin, wallClockMinutes(event.end, day, zone))
+
 /** True if this event overlaps the calendar [day] in [zone] (any portion). */
 internal fun EventInstance.coversDay(day: LocalDate, zone: TimeZone): Boolean {
     if (isAllDay) {
@@ -392,14 +471,14 @@ internal fun layoutDay(
             if (ev.start == ev.end) {
                 // Instant event: keep only if the point falls inside this day.
                 if (ev.start < dayStart || ev.start >= dayEnd) return@mapNotNull null
-                val m = (ev.start - dayStart).inWholeMinutes.toInt().coerceIn(0, MINUTES_PER_DAY)
+                val m = wallClockMinutes(ev.start, day, zone)
                 Raw(ev, m, m)
             } else {
                 val s = maxOf(ev.start, dayStart)
                 val e = minOf(ev.end, dayEnd)
                 if (e <= s) return@mapNotNull null
-                val startMin = (s - dayStart).inWholeMinutes.toInt().coerceIn(0, MINUTES_PER_DAY)
-                val endMin = (e - dayStart).inWholeMinutes.toInt().coerceIn(startMin, MINUTES_PER_DAY)
+                val startMin = wallClockMinutes(s, day, zone)
+                val endMin = wallClockEndMinutes(startMin, s, e, day, zone).coerceAtMost(MINUTES_PER_DAY)
                 Raw(ev, startMin, endMin)
             }
         }