diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 63eaf70b..bb448297 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,9 +1,10 @@
-**3.0.16 - 10/31/24**
+**3.0.16 - 10/30/24**
 
   - Bugfix to prevent a LookupTable from changing order of the value columns
   - Fix mypy errors in vivarium/framework/lookup/table.py
   - Typing changes in vivarium/framework/lookup/interpolation.py
   - Fix broken build from LayeredConfigTree typing
+  - Fix type handling for clock and step size in vivarium/framework/event.py
 
 **3.0.15 - 10/24/24**
 
diff --git a/src/vivarium/framework/event.py b/src/vivarium/framework/event.py
index d5805970..075f2d81 100644
--- a/src/vivarium/framework/event.py
+++ b/src/vivarium/framework/event.py
@@ -30,7 +30,7 @@
 from __future__ import annotations
 
 from collections.abc import Callable
-from datetime import datetime
+from datetime import datetime, timedelta
 from typing import TYPE_CHECKING, Any, NamedTuple
 
 import pandas as pd
@@ -115,11 +115,24 @@ def emit(self, index: pd.Index[int], user_data: dict[str, Any] | None = None) ->
         """
         if not user_data:
             user_data = {}
+
+        clock = self.manager.clock()
+        step_size = self.manager.step_size()
+        event_time: ClockTime
+        if isinstance(clock, int) and isinstance(step_size, int):
+            event_time = clock + step_size
+        elif isinstance(clock, datetime) and isinstance(step_size, timedelta):
+            event_time = clock + step_size
+        else:
+            raise ValueError(
+                f"Clock ({type(clock)}) and step size ({type(step_size)}) are not compatible."
+            )
+
         e = Event(
             index,
             user_data,
-            self.manager.clock() + self.manager.step_size(),  # type: ignore[operator, arg-type]
-            self.manager.step_size(),
+            event_time,
+            step_size,
         )
 
         for priority_bucket in self.listeners:
diff --git a/src/vivarium/types.py b/src/vivarium/types.py
index cc902455..5d813e31 100644
--- a/src/vivarium/types.py
+++ b/src/vivarium/types.py
@@ -19,8 +19,8 @@
     float,
     int,
 ]
-# todo need to use TypeVars here
+# TODO: [MIC-5481] need to use TypeVars here
 Time = Union[pd.Timestamp, datetime]
 Timedelta = Union[pd.Timedelta, timedelta]
-ClockTime = Union[Time, Number]
-ClockStepSize = Union[Timedelta, Number]
+ClockTime = Union[Time, int]
+ClockStepSize = Union[Timedelta, int]