Detect changes in Blender object for more efficient export script

I have a Blender file called Assets.blend containing over 100 objects for a game I’m developing in Unity. When ever I make modifications, I run a script that exports each root object as a separate fbx file. However I have no way of detecting which ones have been updated, so every time I have to re-export every single object even though I’ve only created/modified 1. The time it takes to run the script is about 10 seconds, but then Unity detects the changes and spends over 30 seconds processing mostly unchanged prefabs.

How can I improve my script so that it knows which objects have been altered since the last export? There does not appear to be any date_modified variable for objects or meshes.

EDIT: Sorry for the double thread post, I waited a day for my first post to show up before trying again, I figured it didn’t go through.