diff --git a/backend/open_webui/models/calendar.py b/backend/open_webui/models/calendar.py
index 36651536e7..2067ccfab5 100644
--- a/backend/open_webui/models/calendar.py
+++ b/backend/open_webui/models/calendar.py
@@ -695,35 +695,34 @@ class CalendarEventTable:
         self,
         now_ns: int,
         default_lookahead_ns: int,
+        grace_ns: int = 0,
         db: Optional[AsyncSession] = None,
     ) -> list[tuple[CalendarEventModel, Optional[str]]]:
         """Events starting between now and now + lookahead, for alert processing.
 
         Per-event lookahead is read from meta.alert_minutes (falls back to
         default_lookahead_ns).  Returns (event, user_timezone) pairs.
+
+        *grace_ns* widens the SQL lower bound so that events whose start_at
+        is up to *grace_ns* nanoseconds in the past are still fetched.  This
+        ensures "At time of event" alerts (alert_minutes=0) are not missed
+        when the scheduler polls a few seconds after the event's exact start
+        time.
         """
         from open_webui.models.users import User as UserRow
-        from open_webui.utils.automations import SCHEDULER_POLL_INTERVAL
 
         # Use the maximum possible lookahead (60 min) to cast a wide net;
         # per-event filtering happens in Python after fetching.
         max_lookahead_ns = max(default_lookahead_ns, 60 * 60 * 1_000_000_000)
         upper = now_ns + max_lookahead_ns
 
-        # Grace window: allow events whose start_at is up to one poll cycle
-        # in the past.  This ensures "At time of event" alerts (alert_minutes=0)
-        # are not missed when the scheduler polls a few seconds after the
-        # event's exact start time.
-        grace_ns = (SCHEDULER_POLL_INTERVAL + 5) * 1_000_000_000
-        lower = now_ns - grace_ns
-
         async with get_async_db_context(db) as db:
             result = await db.execute(
                 select(CalendarEvent, UserRow.timezone)
                 .outerjoin(UserRow, UserRow.id == CalendarEvent.user_id)
                 .filter(
                     CalendarEvent.is_cancelled == False,
-                    CalendarEvent.start_at >= lower,
+                    CalendarEvent.start_at >= now_ns - grace_ns,
                     CalendarEvent.start_at <= upper,
                 )
             )
@@ -741,9 +740,7 @@ class CalendarEventTable:
                 if alert_minutes < 0:
                     # alert_minutes < 0 means "no alert"
                     continue
-                # For "at time of event" (0 minutes), use the grace window
-                # so events that just started are still captured.
-                event_lookahead_ns = max(alert_minutes * 60 * 1_000_000_000, grace_ns)
+                event_lookahead_ns = alert_minutes * 60 * 1_000_000_000
             else:
                 event_lookahead_ns = default_lookahead_ns
 
diff --git a/backend/open_webui/utils/automations.py b/backend/open_webui/utils/automations.py
index 1097a308ed..c0b119d9c2 100644
--- a/backend/open_webui/utils/automations.py
+++ b/backend/open_webui/utils/automations.py
@@ -500,9 +500,14 @@ async def _check_calendar_alerts(app) -> None:
 
     now_ns = int(time.time_ns())
     default_lookahead_ns = CALENDAR_ALERT_LOOKAHEAD_MINUTES * 60 * 1_000_000_000
+    # Grace window covers one poll cycle + jitter so "At time of event"
+    # alerts (alert_minutes=0) are not missed.
+    grace_ns = (SCHEDULER_POLL_INTERVAL + 5) * 1_000_000_000
 
     async with get_async_db() as db:
-        upcoming = await CalendarEvents.get_upcoming_events(now_ns, default_lookahead_ns, db=db)
+        upcoming = await CalendarEvents.get_upcoming_events(
+            now_ns, default_lookahead_ns, grace_ns=grace_ns, db=db
+        )
 
     if not upcoming:
         return