So, I tried something like that, but the result was it would increment the time by five hours each time the copy is edited since the time of existing spot copies is NOT reformatted to Chicago time on the edit form. 
This was one of the things I copied directly from expire_on. Do we know why this function is here in the first place? It looks like whenever we check these datetimes, we use datetime.datetime.now(), which I think uses the local time, so it seems like we shouldn't be converting to UTC in the first place.