diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncoding.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncoding.kt
index 446489c..adaeb0c 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncoding.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncoding.kt
@@ -1,11 +1,10 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
-import java.time.Instant
+import de.jeanlucmakiola.calendula.domain.reminders.allDayLeadDays
 import java.time.LocalDate
 import java.time.LocalTime
 import java.time.ZoneId
 import java.time.ZoneOffset
-import java.time.temporal.ChronoUnit
 
 /**
  * Translates an all-day reminder between the **semantic** lead time the UI
@@ -73,19 +72,14 @@ internal fun nextYearlyOccurrence(month: Int, day: Int, today: LocalDate): Local
 
 /**
  * Recover the semantic whole-day lead time from a raw all-day reminder
- * [rawMinutes]. Keys off the **local date** of the encoded fire instant, so it
- * returns the right day count regardless of which [timeOfDayMinutes] wrote the
- * row — including pre-feature rows (raw multiples of 1440, fired at UTC midnight)
- * and rows written under a different timezone. A negative [rawMinutes] (fire
- * after DTSTART) folds to day 0.
+ * [rawMinutes] — the inverse of [toProviderAllDayMinutes], for the form and the
+ * detail screen. Delegates to [allDayLeadDays] so what is displayed is the day
+ * the reminder actually fires on; see there for how an encoded row is told from
+ * a plain one written by another calendar app.
  */
 internal fun fromProviderAllDayMinutes(
     rawMinutes: Int,
     startDate: LocalDate,
     zone: ZoneId,
-): Int {
-    val utcMidnight = startDate.atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
-    val fireLocalDate = Instant.ofEpochMilli(utcMidnight - rawMinutes * MILLIS_PER_MINUTE)
-        .atZone(zone).toLocalDate()
-    return ChronoUnit.DAYS.between(fireLocalDate, startDate).toInt() * MINUTES_PER_DAY
-}
+    timeOfDayMinutes: Int,
+): Int = allDayLeadDays(rawMinutes, startDate, zone, timeOfDayMinutes).toInt() * MINUTES_PER_DAY
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
index 499b956..17e62ee 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
@@ -54,7 +54,12 @@ import javax.inject.Singleton
 interface CalendarDataSource {
     fun calendars(): List<CalendarSource>
     fun instances(beginMillis: Long, endMillis: Long): List<EventInstance>
-    fun eventDetail(eventId: Long): EventDetail?
+    /**
+     * [allDayReminderTimeMinutes]: the hour all-day reminders fire at, needed to
+     * decode their stored offsets back to whole-day lead times (see
+     * [fromProviderAllDayMinutes]).
+     */
+    fun eventDetail(eventId: Long, allDayReminderTimeMinutes: Int): EventDetail?
 
     /**
      * Master/one-off events whose title, description or location contains
@@ -670,7 +675,7 @@ class AndroidCalendarDataSource @Inject constructor(
         }
     }
 
-    override fun eventDetail(eventId: Long): EventDetail? {
+    override fun eventDetail(eventId: Long, allDayReminderTimeMinutes: Int): EventDetail? {
         val attendees = queryAttendees(eventId)
         val reminders = queryReminders(eventId)
         return resolver.query(
@@ -679,7 +684,9 @@ class AndroidCalendarDataSource @Inject constructor(
             null, null, null,
         )?.use { c ->
             if (!c.moveToFirst()) null
-            else CursorColumnReader(c).toEventDetailCore(attendees, reminders)
+            else CursorColumnReader(c).toEventDetailCore(
+                attendees, reminders, allDayReminderTimeMinutes,
+            )
         }
     }
 
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt
index 19dcb5a..9d57346 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt
@@ -179,7 +179,8 @@ class CalendarRepositoryImpl @Inject constructor(
     }
 
     override suspend fun eventDetail(eventId: Long): EventDetail = withContext(io) {
-        dataSource.eventDetail(eventId) ?: throw NoSuchEventException(eventId)
+        dataSource.eventDetail(eventId, allDayReminderTimeMinutes())
+            ?: throw NoSuchEventException(eventId)
     }
 
     override suspend fun searchEvents(query: String): List<EventInstance> = withContext(io) {
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt
index 3711c81..cbf572d 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt
@@ -24,6 +24,7 @@ private const val TAG = "EventDetailMapper"
 internal fun ColumnReader.toEventDetailCore(
     attendees: List<Attendee>,
     reminders: List<Reminder>,
+    allDayReminderTimeMinutes: Int,
 ): EventDetail? {
     // DTSTART is epoch millis in UTC, so a series anchored before 1970 (common
     // for yearly birthdays/anniversaries synced over CalDAV) is legitimately
@@ -89,7 +90,13 @@ internal fun ColumnReader.toEventDetailCore(
     val displayReminders = if (isAllDay) {
         val startDate = Instant.ofEpochMilli(begin).atZone(ZoneOffset.UTC).toLocalDate()
         val zone = ZoneId.systemDefault()
-        reminders.map { it.copy(minutes = fromProviderAllDayMinutes(it.minutes, startDate, zone)) }
+        reminders.map {
+            it.copy(
+                minutes = fromProviderAllDayMinutes(
+                    it.minutes, startDate, zone, allDayReminderTimeMinutes,
+                ),
+            )
+        }
     } else {
         reminders
     }
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderActionReceiver.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderActionReceiver.kt
index 53c883b..20d5221 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderActionReceiver.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderActionReceiver.kt
@@ -3,6 +3,7 @@ package de.jeanlucmakiola.calendula.data.reminders
 import android.content.BroadcastReceiver
 import android.content.Context
 import android.content.Intent
+import androidx.core.net.toUri
 import dagger.hilt.android.AndroidEntryPoint
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import kotlinx.coroutines.CoroutineScope
@@ -91,10 +92,19 @@ class ReminderActionReceiver : BroadcastReceiver() {
         private const val EXTRA_LOCATION = "location"
         private const val EXTRA_ALL_DAY = "all_day"
 
-        /** An explicit intent to this receiver carrying [alert] as extras. */
+        /**
+         * An explicit intent to this receiver carrying [alert] as extras.
+         *
+         * The data URI names the reminder and carries no information the extras
+         * don't. It is what actually keeps two reminders' `PendingIntent`s
+         * apart: `filterEquals` compares action, component, data, type and
+         * categories — never extras — so without it a request-code collision
+         * would have them share one alarm and one payload.
+         */
         fun intent(context: Context, action: String, alert: ReminderAlert): Intent =
             Intent(context, ReminderActionReceiver::class.java).apply {
                 this.action = action
+                data = "calendula://reminder/${alert.key}".toUri()
                 putExtra(EXTRA_ALERT_KEY, alert.key)
                 putExtra(EXTRA_EVENT_ID, alert.eventId)
                 putExtra(EXTRA_CALENDAR_ID, alert.calendarId)
@@ -110,9 +120,9 @@ class ReminderActionReceiver : BroadcastReceiver() {
          * PendingIntents stay distinct and don't clobber each other.
          *
          * The key is a hash now rather than a small row id, so the shift is what
-         * keeps the action slot intact; the top three bits it drops only make two
-         * *different* reminders collide, which the intent extras then separate
-         * (PendingIntents compare their intents too, not just the request code).
+         * keeps the action slot intact; the top three bits it drops can make two
+         * *different* reminders share a code, which the per-reminder data URI in
+         * [intent] separates.
          */
         fun requestCode(alert: ReminderAlert, action: String): Int {
             val actionOffset = when (action) {
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlan.kt b/app/src/main/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlan.kt
index e098b3f..134c8fb 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlan.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlan.kt
@@ -124,30 +124,59 @@ private fun allDayDate(beginMillis: Long): LocalDate =
 /**
  * How many whole days before its occurrence a raw all-day offset means.
  *
- * A plain multiple of 1440 is read at face value. That covers rows from other
- * calendar apps, which carry no encoded hour — and it stays right for our own
- * rows that happen to land on a multiple, because those encode a wall-clock hour
- * equal to the sampled UTC offset, so the day count is the same either way.
+ * Normally the local date of the encoded fire instant answers it: our own rows
+ * fold the wanted hour into the offset, so that date *is* the day the reminder
+ * belongs to, whatever the offset was when it was written.
  *
- * Anything else is one of ours, with an hour folded in: recover the day count the
- * way [de.jeanlucmakiola.calendula.data.calendar.fromProviderAllDayMinutes]
- * does for display, by asking which local date the encoded instant falls on.
- * Keeping the two in step is what makes the notification arrive on the day the
- * event screen says it will.
+ * A plain multiple of 1440 is the exception. Those come from calendar apps that
+ * store a bare lead time against UTC midnight, and east of UTC both readings
+ * agree anyway — but west of UTC the instant falls on the previous local date,
+ * so the day count has to be taken at face value or it comes out one too many.
+ *
+ * Except when the row is one of ours after all: our offset lands on a multiple
+ * whenever the all-day hour equals the zone's UTC offset (20:00 in New York,
+ * 19:00 an hour further west, and so on), and reading those at face value fired
+ * them a day late — a "1 day before" arriving on the morning of the event. So
+ * the hour decides, not the shape of the number: an instant landing on the hour
+ * the setting names is ours. Within an hour or so of it counts, because a fixed
+ * offset written in one DST phase drifts by the offset delta in the other.
+ *
+ * The two are genuinely indistinguishable in that band — the encodings collide
+ * exactly there — so the tie goes to the reading that honours the lead time the
+ * user chose in this app.
+ *
+ * [de.jeanlucmakiola.calendula.data.calendar.fromProviderAllDayMinutes] calls
+ * this for display, so the notification arrives on the day the event screen says
+ * it will.
  */
-internal fun allDayLeadDays(rawMinutes: Int, beginMillis: Long, zone: ZoneId): Long {
-    if (rawMinutes % MINUTES_PER_DAY == 0) return (rawMinutes / MINUTES_PER_DAY).toLong()
-    val encoded = Instant.ofEpochMilli(beginMillis - rawMinutes * MILLIS_PER_MINUTE)
-    return ChronoUnit.DAYS.between(encoded.atZone(zone).toLocalDate(), allDayDate(beginMillis))
+internal fun allDayLeadDays(
+    rawMinutes: Int,
+    startDate: LocalDate,
+    zone: ZoneId,
+    allDayTimeMinutes: Int,
+): Long {
+    val utcMidnight = startDate.atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
+    val encoded = Instant.ofEpochMilli(utcMidnight - rawMinutes * MILLIS_PER_MINUTE).atZone(zone)
+    val minutesFromNamedHour = encoded.toLocalTime().let {
+        val delta = (it.hour * 60 + it.minute - allDayTimeMinutes).mod(MINUTES_PER_DAY)
+        minOf(delta, MINUTES_PER_DAY - delta)
+    }
+    if (rawMinutes % MINUTES_PER_DAY == 0 && minutesFromNamedHour > NAMED_HOUR_TOLERANCE_MINUTES) {
+        return (rawMinutes / MINUTES_PER_DAY).toLong()
+    }
+    return ChronoUnit.DAYS.between(encoded.toLocalDate(), startDate)
 }
 
+/** DST drift a row written in the other phase carries, rounded up past Lord Howe's half hour. */
+private const val NAMED_HOUR_TOLERANCE_MINUTES = 90
+
 private fun allDayAlarmMillis(
     beginMillis: Long,
     rawMinutes: Int,
     zone: ZoneId,
     allDayTimeMinutes: Int,
 ): Long = allDayDate(beginMillis)
-    .minusDays(allDayLeadDays(rawMinutes, beginMillis, zone))
+    .minusDays(allDayLeadDays(rawMinutes, allDayDate(beginMillis), zone, allDayTimeMinutes))
     .atTime(LocalTime.of(allDayTimeMinutes / 60, allDayTimeMinutes % 60))
     .atZone(zone)
     .toInstant()
@@ -214,6 +243,16 @@ fun reminderWatermark(lastScanMillis: Long?, nowMillis: Long): Long =
  * reminder in time: the plain lookahead plus the longest offset any reminder row
  * carries, so a "two weeks before" reminder is planned before it comes due
  * instead of firing late (the limitation Etar's equivalent documents).
+ *
+ * The stretch is capped at [MAX_REMINDER_LEAD_MILLIS]. `maxReminderMinutes` is
+ * whatever the largest row in the whole provider says, across every calendar and
+ * whoever wrote it — an imported `TRIGGER:-P100W`, or a sync adapter writing
+ * nonsense, would otherwise make every scan (launch, every provider change, every
+ * alarm) expand every recurring series over years. A lead beyond the cap is not
+ * delivered; a year is far past anything the picker composes.
  */
 fun reminderQueryHorizon(lookaheadMillis: Long, maxReminderMinutes: Int): Long =
-    lookaheadMillis + maxOf(0L, maxReminderMinutes * MILLIS_PER_MINUTE)
+    lookaheadMillis + (maxReminderMinutes * MILLIS_PER_MINUTE).coerceIn(0L, MAX_REMINDER_LEAD_MILLIS)
+
+/** Longest reminder offset a scan stretches its query window for — one year. */
+const val MAX_REMINDER_LEAD_MILLIS = 365L * 24 * 60 * 60 * 1000
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/ui/RootScreen.kt b/app/src/main/java/de/jeanlucmakiola/calendula/ui/RootScreen.kt
index 33385ff..83d432e 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/ui/RootScreen.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/ui/RootScreen.kt
@@ -51,6 +51,10 @@ fun RootScreen(
         )
     }
 
+    // Whether the app came up already holding it — a launch scan has covered
+    // that case, so only a grant made during this session owes a re-scan.
+    val grantedAtLaunch = remember { hasPermission }
+
     val lifecycle = LocalLifecycleOwner.current.lifecycle
     DisposableEffect(lifecycle) {
         val obs = LifecycleEventObserver { _, event ->
@@ -88,7 +92,10 @@ fun RootScreen(
             // Runs on entry however the permission was granted — including from
             // Android's app-settings screen, which only comes back through the
             // ON_RESUME check above. Cheap once there is nothing left to do.
-            LaunchedEffect(Unit) { visibilityNotice.reconcile() }
+            LaunchedEffect(Unit) {
+                visibilityNotice.reconcile()
+                if (!grantedAtLaunch) reminderOnboarding.rearmAfterGrant()
+            }
             if (onboardingDone == true && noticePending) {
                 CalendarVisibilityNoticeDialog(onDismiss = visibilityNotice::dismiss)
             }
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsViewModel.kt b/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsViewModel.kt
index 3a005c0..3f2fc3f 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsViewModel.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsViewModel.kt
@@ -153,9 +153,12 @@ class CalendarsViewModel @Inject constructor(
      * reminders. Nothing is patched by hand — the provider notifies and the
      * observer re-queries.
      *
-     * Nothing has to be re-posted on the way back on: reminder delivery plans
-     * from `Instances` and `Reminders` on every scan (#75), and the provider
-     * change this write makes triggers one.
+     * A reminder that came due while the calendar was off stays gone when it is
+     * switched back on. Delivery plans from `Instances` and `Reminders` on every
+     * scan (#75), but the watermark has already moved past that moment, so no
+     * scan returns it again — and on a read-only install the switch never
+     * reaches the provider at all, so nothing even triggers one. Deliberate: the
+     * reminder was silenced on purpose, and the event itself is back in view.
      */
     fun setCalendarVisible(id: Long, visible: Boolean) = write {
         repository.setCalendarsVisible(listOf(id), visible)
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/ui/permission/ReminderOnboardingViewModel.kt b/app/src/main/java/de/jeanlucmakiola/calendula/ui/permission/ReminderOnboardingViewModel.kt
index e20bf7b..f2570c0 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/ui/permission/ReminderOnboardingViewModel.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/ui/permission/ReminderOnboardingViewModel.kt
@@ -4,6 +4,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
+import de.jeanlucmakiola.calendula.data.reminders.ReminderScanner
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.map
@@ -19,6 +20,7 @@ import javax.inject.Inject
 @HiltViewModel
 class ReminderOnboardingViewModel @Inject constructor(
     private val prefs: SettingsPrefs,
+    private val scanner: ReminderScanner,
 ) : ViewModel() {
 
     val onboardingDone: StateFlow<Boolean?> = prefs.reminderOnboardingDone
@@ -34,6 +36,19 @@ class ReminderOnboardingViewModel @Inject constructor(
         viewModelScope.launch {
             prefs.setRemindersEnabled(remindersEnabled)
             prefs.setReminderOnboardingDone()
+            // Nothing else re-arms the scan: turning reminders off cancels the
+            // alarm, so a later "on" would sit without one until a provider
+            // change or the daily worker happened to run (#75).
+            scanner.scan()
         }
     }
+
+    /**
+     * Re-scan after the calendar permission is granted. The launch scan runs
+     * before the grant and bails out without arming anything, so without this
+     * the first alarm waits on the daily worker.
+     */
+    fun rearmAfterGrant() {
+        scanner.scanInBackground()
+    }
 }
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsViewModel.kt b/app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsViewModel.kt
index 9adcf3a..8388991 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsViewModel.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsViewModel.kt
@@ -27,6 +27,7 @@ import de.jeanlucmakiola.calendula.data.prefs.SpecialDatesStalledReason
 import de.jeanlucmakiola.calendula.data.prefs.ThemeMode
 import de.jeanlucmakiola.calendula.data.prefs.TimeFormatPref
 import de.jeanlucmakiola.calendula.data.prefs.WeekStartPref
+import de.jeanlucmakiola.calendula.data.reminders.ReminderScanner
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.FontRole
@@ -68,6 +69,7 @@ class SettingsViewModel @Inject constructor(
     private val specialDatesEngine: SpecialDatesSyncEngine,
     specialDatesSpec: SpecialDatesCalendarSpec,
     private val launcherNameManager: LauncherNameManager,
+    private val reminderScanner: ReminderScanner,
     @IoDispatcher private val io: CoroutineDispatcher,
     @ApplicationContext private val appContext: Context,
 ) : ViewModel() {
@@ -582,8 +584,16 @@ class SettingsViewModel @Inject constructor(
         viewModelScope.launch { prefs.setDrawerViewOrder(order) }
     }
 
+    /**
+     * A scan follows the write, in that order. Switching reminders off cancels
+     * the scan alarm, so switching them back on has to arm a new one — nothing
+     * else would until a provider change or the daily worker came along (#75).
+     */
     fun setRemindersEnabled(enabled: Boolean) {
-        viewModelScope.launch { prefs.setRemindersEnabled(enabled) }
+        viewModelScope.launch {
+            prefs.setRemindersEnabled(enabled)
+            reminderScanner.scan()
+        }
     }
 
     fun setAutofocusEventTitle(enabled: Boolean) {
@@ -598,8 +608,12 @@ class SettingsViewModel @Inject constructor(
         viewModelScope.launch { prefs.setDefaultAllDayReminderMinutes(minutes) }
     }
 
+    /** The armed alarm was planned for the old hour, so re-plan against the new one. */
     fun setAllDayReminderTimeMinutes(minutesOfDay: Int) {
-        viewModelScope.launch { prefs.setAllDayReminderTimeMinutes(minutesOfDay) }
+        viewModelScope.launch {
+            prefs.setAllDayReminderTimeMinutes(minutesOfDay)
+            reminderScanner.scan()
+        }
     }
 
     fun setSnoozeMinutes(minutes: Int) {
diff --git a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncodingTest.kt b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncodingTest.kt
index 7ebb69b..0dd4cc4 100644
--- a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncodingTest.kt
+++ b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncodingTest.kt
@@ -54,7 +54,8 @@ class AllDayReminderEncodingTest {
             for (time in listOf(0, nineAm, 20 * 60)) {
                 for (semantic in listOf(0, 1_440, 2_880, 10_080)) {
                     val raw = toProviderAllDayMinutes(semantic, date, berlin, time)
-                    assertThat(fromProviderAllDayMinutes(raw, date, berlin)).isEqualTo(semantic)
+                    assertThat(fromProviderAllDayMinutes(raw, date, berlin, time))
+                        .isEqualTo(semantic)
                 }
             }
         }
@@ -64,9 +65,31 @@ class AllDayReminderEncodingTest {
     fun `pre-feature rows (raw multiple of 1440) still decode to whole days`() {
         // Reminders written before this feature stored raw N*1440 (fired at UTC
         // midnight). They must still read back as "N days before".
-        assertThat(fromProviderAllDayMinutes(1_440, summer, berlin)).isEqualTo(1_440)
-        assertThat(fromProviderAllDayMinutes(1_440, winter, berlin)).isEqualTo(1_440)
-        assertThat(fromProviderAllDayMinutes(2_880, summer, berlin)).isEqualTo(2_880)
+        assertThat(fromProviderAllDayMinutes(1_440, summer, berlin, nineAm)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(1_440, winter, berlin, nineAm)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(2_880, summer, berlin, nineAm)).isEqualTo(2_880)
+    }
+
+    @Test
+    fun `an offset that encodes to a multiple still decodes to its own lead time`() {
+        // New York at 20:00 is the collision: "1 day before" encodes to a plain 0,
+        // which read at face value would say "at time of event". The screen has to
+        // show what the reminder does, which is fire the evening before.
+        val newYork = ZoneId.of("America/New_York")
+        val eightPm = 20 * 60
+        val raw = toProviderAllDayMinutes(1_440, summer, newYork, eightPm)
+
+        assertThat(raw).isEqualTo(0)
+        assertThat(fromProviderAllDayMinutes(raw, summer, newYork, eightPm)).isEqualTo(1_440)
+    }
+
+    @Test
+    fun `a foreign multiple west of UTC keeps its face-value lead time`() {
+        // No encoded hour in this row, and its instant lands on the evening two
+        // days out in New York — the local-date reading would say "2 days before".
+        val newYork = ZoneId.of("America/New_York")
+
+        assertThat(fromProviderAllDayMinutes(1_440, summer, newYork, nineAm)).isEqualTo(1_440)
     }
 
     @Test
@@ -74,8 +97,8 @@ class AllDayReminderEncodingTest {
         val atNine = toProviderAllDayMinutes(1_440, summer, berlin, nineAm)
         val atEight = toProviderAllDayMinutes(1_440, summer, berlin, 8 * 60)
         assertThat(atNine).isNotEqualTo(atEight)
-        assertThat(fromProviderAllDayMinutes(atNine, summer, berlin)).isEqualTo(1_440)
-        assertThat(fromProviderAllDayMinutes(atEight, summer, berlin)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(atNine, summer, berlin, nineAm)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(atEight, summer, berlin, nineAm)).isEqualTo(1_440)
     }
 
     @Test
diff --git a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapperTest.kt b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapperTest.kt
index 36d397d..3b4203c 100644
--- a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapperTest.kt
+++ b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapperTest.kt
@@ -79,7 +79,8 @@ class EventDetailMapperTest {
     private fun MapColumnReader.toDetail(
         attendees: List<de.jeanlucmakiola.calendula.domain.Attendee> = emptyList(),
         reminders: List<Reminder> = emptyList(),
-    ) = toEventDetailCore(attendees, reminders)
+        allDayReminderTimeMinutes: Int = 9 * 60,
+    ) = toEventDetailCore(attendees, reminders, allDayReminderTimeMinutes)
 
     @Test
     fun `happy path detail maps all fields and embeds matching EventInstance`() {
diff --git a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/FakeCalendarDataSource.kt b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/FakeCalendarDataSource.kt
index ccc9b68..89f96ae 100644
--- a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/FakeCalendarDataSource.kt
+++ b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/FakeCalendarDataSource.kt
@@ -72,7 +72,8 @@ internal class FakeCalendarDataSource : CalendarDataSource {
     override fun instances(beginMillis: Long, endMillis: Long): List<EventInstance> =
         instancesResult(beginMillis, endMillis)
     override fun searchEvents(query: String): List<EventInstance> = searchResult(query)
-    override fun eventDetail(eventId: Long): EventDetail? = eventDetailResult(eventId)
+    override fun eventDetail(eventId: Long, allDayReminderTimeMinutes: Int): EventDetail? =
+        eventDetailResult(eventId)
     override fun eventColorPalette(calendarId: Long): List<EventColorOption> =
         eventColorPaletteResult(calendarId)
     override fun exportableEvents(calendarIds: Set<Long>?): List<IcsEvent> {
diff --git a/app/src/test/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlanTest.kt b/app/src/test/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlanTest.kt
index 8dcd1c1..cf17e91 100644
--- a/app/src/test/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlanTest.kt
+++ b/app/src/test/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlanTest.kt
@@ -184,8 +184,58 @@ class ReminderPlanTest {
 
     @Test
     fun `a zero-day row fires on the event's own date`() {
-        assertThat(allDayLeadDays(rawMinutes = 0, beginMillis = allDayBegin("2026-07-15"), zone = berlin))
-            .isEqualTo(0L)
+        assertThat(
+            allDayLeadDays(
+                rawMinutes = 0,
+                startDate = LocalDate.parse("2026-07-15"),
+                zone = berlin,
+                allDayTimeMinutes = nineAm,
+            ),
+        ).isEqualTo(0L)
+    }
+
+    @Test
+    fun `our own row that encodes to a multiple is not read at face value`() {
+        // New York with the all-day hour at 20:00: "1 day before" encodes to a
+        // plain 0, because 20:00 EDT *is* UTC midnight. Read at face value it
+        // fired at 20:00 on the day of the event instead of the evening before.
+        val newYork = ZoneId.of("America/New_York")
+        val eightPm = 20 * 60
+        val row = encodedAllDayMinutes("2026-07-15", days = 1, timeOfDayMinutes = eightPm, zone = newYork)
+        assertThat(row % 1_440).isEqualTo(0)
+
+        val alarm = plan(
+            instances = listOf(
+                instance(1L, beginMillis = allDayBegin("2026-07-15"), isAllDay = true),
+            ),
+            minutesByEvent = mapOf(1L to listOf(row)),
+            zone = newYork,
+            allDayTimeMinutes = eightPm,
+        ).single().alarmMillis
+
+        assertThat(firedAt(alarm, newYork).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-07-14").atTime(20, 0))
+    }
+
+    @Test
+    fun `such a row keeps its lead time across the DST boundary that wrote it`() {
+        // Same row, sampled in EDT, on a winter occurrence: its instant lands an
+        // hour off the named hour, which still has to read as "one of ours".
+        val newYork = ZoneId.of("America/New_York")
+        val eightPm = 20 * 60
+        val summerRow = encodedAllDayMinutes("2026-07-15", days = 1, timeOfDayMinutes = eightPm, zone = newYork)
+
+        val alarm = plan(
+            instances = listOf(
+                instance(1L, beginMillis = allDayBegin("2027-01-15"), isAllDay = true),
+            ),
+            minutesByEvent = mapOf(1L to listOf(summerRow)),
+            zone = newYork,
+            allDayTimeMinutes = eightPm,
+        ).single().alarmMillis
+
+        assertThat(firedAt(alarm, newYork).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2027-01-14").atTime(20, 0))
     }
 
     @Test
@@ -437,6 +487,17 @@ class ReminderPlanTest {
             .isEqualTo(7 * day + 14 * day)
     }
 
+    @Test
+    fun `the query horizon is capped against an outlier row`() {
+        // The longest offset comes from any row in the provider — an imported
+        // TRIGGER:-P100W would otherwise expand every series over two years, on
+        // every scan.
+        val hundredWeeks = 100 * 7 * 24 * 60
+
+        assertThat(reminderQueryHorizon(lookaheadMillis = 7 * day, maxReminderMinutes = hundredWeeks))
+            .isEqualTo(7 * day + MAX_REMINDER_LEAD_MILLIS)
+    }
+
     @Test
     fun `a first-ever scan starts from now, not from the epoch`() {
         // Otherwise an install — or the upgrade onto in-house delivery — treats
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index d84f2eb..41c4a17 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -175,7 +175,12 @@ an app update or a doze window costs nothing. A first-ever scan claims the
 present rather than the epoch, and a watermark left in the future by a clock
 change is clamped. Every trigger runs the same idempotent `scan()`, so there is
 no ordering between them to get wrong; `BOOT_COMPLETED` and `MY_PACKAGE_REPLACED`
-matter because both wipe pending alarms.
+matter because both wipe pending alarms. Turning reminders off cancels the alarm
+and granting the calendar permission arms none, so those transitions scan too —
+without it, switching reminders back on would sit silent until the daily worker.
+The window a scan reads is the 7-day lookahead plus the longest reminder offset
+in the provider, capped at a year: that offset is whatever the largest row says,
+including one imported from a stray `TRIGGER:-P100W`.
 
 **All-day reminders fire at the hour the setting names.** The stored offset is
 not a plain lead time — `AllDayReminderEncoding` folds a wall-clock hour into it,
@@ -183,7 +188,13 @@ sampled against one date's UTC offset — so taking it at face value drifts by t
 offset delta across a DST boundary, and rows from other apps carry no hour at
 all. The offset is therefore read only for *which day* it means; the hour comes
 from the global all-day reminder setting, recomposed against each occurrence's
-own date. Timed reminders need none of this: `begin` is an absolute instant.
+own date. Which day that is comes from the local date the encoded instant falls
+on — except for a plain multiple of 1440, read at face value because a foreign
+row means literal days from UTC midnight. The two collide where the all-day hour
+equals the zone's UTC offset (20:00 in New York), and there the instant landing
+on the named hour decides it is ours; the display path decodes through the same
+function, so the screen and the notification agree. Timed reminders need none of
+this: `begin` is an absolute instant.
 
 **One visibility model.** The scan only plans occurrences of calendars with
 `Calendars.VISIBLE = 1`, and that flag *is* the app's on/off switch: Settings →