[Chychy]

It might be easier if we store timestamp in the database instead of full string (or datetime) and use timestamp to make comparaisons

I'm not sure with your goal on the last commit, do you try to convert local time to the entry's timezone ?

Example :
Local time : 23:00 (+0200)
SQL time : 21:00 (+0000)
You can convert the local time into timestamp and then parse it into any timezone string using "astimezone" on datetime object, it seems simplier, but using timestamps might be even better