diff --git a/src/pyflask/manageNeuroconv/manage_neuroconv.py b/src/pyflask/manageNeuroconv/manage_neuroconv.py
index c3778b8f0..a322b602a 100644
--- a/src/pyflask/manageNeuroconv/manage_neuroconv.py
+++ b/src/pyflask/manageNeuroconv/manage_neuroconv.py
@@ -992,9 +992,10 @@ def update_conversion_progress(message):
                 del ecephys_metadata["ElectrodeColumns"]
 
         # Correct timezone in metadata fields
-        resolved_metadata["NWBFile"]["session_start_time"].replace(tzinfo=zoneinfo.ZoneInfo(info["timezone"]))
+        resolved_metadata["NWBFile"]["session_start_time"] = resolved_metadata["NWBFile"][
+            "session_start_time"].replace(tzinfo=zoneinfo.ZoneInfo(info["timezone"]))
         if "date_of_birth" in resolved_metadata["Subject"]:
-            resolved_metadata["Subject"]["date_of_birth"].replace(tzinfo=zoneinfo.ZoneInfo(info["timezone"]))
+            resolved_metadata["Subject"]["date_of_birth"] = resolved_metadata["Subject"]["date_of_birth"].replace(tzinfo=zoneinfo.ZoneInfo(info["timezone"]))
 
         # Actually run the conversion
         converter.run_conversion(