diff --git a/src/gort/overwatcher/ephemeris.py b/src/gort/overwatcher/ephemeris.py
index 43426d9..86c7e0a 100644
--- a/src/gort/overwatcher/ephemeris.py
+++ b/src/gort/overwatcher/ephemeris.py
@@ -120,23 +120,28 @@ async def update_ephemeris(self, sjd: int | None = None):
 
         return self.ephemeris
 
-    def is_night(self, mode: Literal["normal", "observer"] = "normal"):
+    def is_night(self, mode: Literal["strict", "observer"] = "strict"):
         """Determines whether it is night-time.
 
         Parameters
         ----------
         mode
-            The mode to use. If ``'normal'``, the function will return :obj:`True`
+            The mode to use. If ``'strict'``, the function will return :obj:`True`
             if the current time is between 15-degree twilights. If ``'observer'``,
             it will also return :obj:`False` if we are within
             ``scheduler.stop_secs_before_morning`` seconds of the morning twilight.
+            In this mode it also returns :obj:`True`
+            ``scheduler.open_dome_secs_before_twilight`` seconds before the evening
+            twilight to allow time to open the dome before starting observations.
 
         """
 
         ephemeris = self.ephemeris
         now_jd = float(Time.now().jd)
 
-        stop_secs = self.config["overwatcher.schedule.stop_secs_before_morning"]
+        schedule_config = self.config["overwatcher.schedule"]
+        stop_secs = schedule_config["stop_secs_before_morning"]
+        open_dome_secs = schedule_config["open_dome_secs_before_twilight"]
 
         if not ephemeris:
             self.log.warning("Ephemeris data not available. is_night() returns False.")
@@ -145,6 +150,7 @@ def is_night(self, mode: Literal["normal", "observer"] = "normal"):
         twilight_end = float(ephemeris.twilight_end)
         twilight_start = float(ephemeris.twilight_start)
         if mode == "observer":
+            twilight_end -= open_dome_secs / 86400
             twilight_start -= stop_secs / 86400
 
         return twilight_end < now_jd < twilight_start
@@ -161,7 +167,7 @@ def time_to_evening_twilight(self):
 
         return round(evening_twilight - now, 2)
 
-    def time_to_morning_twilight(self, mode: Literal["normal", "observer"] = "normal"):
+    def time_to_morning_twilight(self, mode: Literal["strict", "observer"] = "strict"):
         """Returns the time to morning twilight in seconds."""
 
         ephemeris = self.ephemeris
diff --git a/src/gort/overwatcher/observer.py b/src/gort/overwatcher/observer.py
index cddc43d..25a15b0 100644
--- a/src/gort/overwatcher/observer.py
+++ b/src/gort/overwatcher/observer.py
@@ -48,9 +48,6 @@ async def task(self):
         state = self.overwatcher.state
         ephemeris = self.overwatcher.ephemeris
 
-        # Number of seconds before evening twilight when to open the dome.
-        open_dome_secs = self.config["overwatcher.schedule.stop_secs_before_morning"]
-
         while True:
             if state.dry_run:
                 pass
@@ -83,16 +80,6 @@ async def task(self):
                     )
                     await asyncio.sleep(15)
 
-            else:
-                # If we are within open_dome_secs_before_twilight seconds
-                # of the evening twilight, open the dome to be ready for observing.
-
-                time_to_twilight = ephemeris.time_to_evening_twilight() or -1
-                if time_to_twilight > 0 and time_to_twilight < open_dome_secs:
-                    if not await self.overwatcher.dome.is_opening():
-                        await self.notify("Opening the dome for observing.")
-                        await self.overwatcher.dome.open()
-
             await asyncio.sleep(self.interval)
 
 
@@ -218,6 +205,18 @@ async def stop_observing(
     async def observe_loop_task(self):
         """Runs the observing loop."""
 
+        # Check that we have not started too early (this happens when we open the dome
+        # a bit early to avoid wasting time). If so, wait until we are properly in
+        # the observing window.
+        if not self.overwatcher.ephemeris.is_night():
+            time_to_twilight = self.overwatcher.ephemeris.time_to_evening_twilight()
+            if time_to_twilight and time_to_twilight > 0:
+                await self.notify(
+                    f"Waiting until evening twilight to start observing "
+                    f"({time_to_twilight:.0f} seconds)."
+                )
+                await asyncio.sleep(time_to_twilight)
+
         await self.gort.cleanup(readout=True)
         observer = self.gort.observer