diff --git a/allensdk/internal/brain_observatory/time_sync.py b/allensdk/internal/brain_observatory/time_sync.py
index d7aa449b6..340f3b25b 100644
--- a/allensdk/internal/brain_observatory/time_sync.py
+++ b/allensdk/internal/brain_observatory/time_sync.py
@@ -58,11 +58,23 @@ def monitor_delay(sync_dset, stim_times, photodiode_key,
     """Calculate monitor delay."""
     try:
         transitions = stim_times[::transition_frame_interval]
-        photodiode_events = get_real_photodiode_events(sync_dset, photodiode_key)
-        transition_events = photodiode_events[0:len(transitions)]
+        photodiode_events = get_real_photodiode_events(sync_dset,
+                                                       photodiode_key)
+        if len(transitions) > len(photodiode_events):
+            logging.warning(
+                "More stimulus transitions counted than "
+                f"photodiode events (transitions={len(transitions)}, "
+                f"events={len(photodiode_events)}). "
+                "Truncating stimulus transitions to length of "
+                "photodiode events.")
+            transitions = transitions[:len(photodiode_events)]
 
-        delay = np.mean(transition_events-transitions)
-        logging.info("Calculated monitor delay: %s", delay)
+        transition_events = photodiode_events[0:len(transitions)]
+        delays = transition_events - transitions
+        delay = np.mean(delays)
+        logging.info(f"Calculated monitor delay: {delay}. \n "
+                     f"Max monitor delay: {np.max(delays)}. \n "
+                     f"Min monitor delay: {np.min(delays)}.")
 
         if delay < 0 or delay > max_monitor_delay:
             delay = assumed_delay
diff --git a/allensdk/test/internal/brain_observatory/test_time_sync.py b/allensdk/test/internal/brain_observatory/test_time_sync.py
index 46f6aeb1a..0a326630a 100644
--- a/allensdk/test/internal/brain_observatory/test_time_sync.py
+++ b/allensdk/test/internal/brain_observatory/test_time_sync.py
@@ -413,6 +413,22 @@ def test_module(input_json):
                            equal_nan=True)
 
 
+@pytest.mark.parametrize(
+    "photodiode_events,stim_events,expected_delay",
+    [
+        (np.array([2, 3, 4, 5]), np.array([1, 2, 3, 4]), ts.ASSUMED_DELAY),
+        (np.array([2.02, 3.02, 4.02, 5.02]), np.array([2., 3., 4., 5.]), 0.02),
+        (np.array([2, 3, 4]), np.array([1, 2, 3, 4]), ts.ASSUMED_DELAY),
+    ]
+)
+def test_monitor_delay_mocked(photodiode_events, stim_events, expected_delay,
+                              monkeypatch):
+    monkeypatch.setattr(ts, "get_real_photodiode_events", lambda x, y: x)
+    assert (ts.monitor_delay(photodiode_events, stim_events, "dummy_key",
+                             transition_frame_interval=1)
+            == pytest.approx(expected_delay, 0.000001))
+
+
 @pytest.mark.skipif(data_skip, reason="No sync or data")
 def test_monitor_delay(scientifica_input):
     sync_file = scientifica_input.pop("sync_file")