Timezones. So, general rules are:

1. If you don't store timezone, always use and assume UTC. Databases, backends, whatever you use, all time must be kept be in UTC.
2. If you store timezones, ensure you store them everywhere and don't drop them anywhere.
3. It's always better to ignore backend server time in favor of database's `now().` Having a single source of truth makes time consistent (if it's the same database, obviously). If you combine backend time and database time, you likely get a violation of causality.

I've just spent a couple of hours investigating "weird random one-hour time drifts on updates." Guys violated all three rules above:
- they didn't store the timezone;
- their servers had inconsistent timezones. Java was in +XX., while the server itself in UTC. On one host, they forgot to put JVM in the same timezone;
- they dropped the timezone because they thought it was the same everywhere, so there was no point in serializing it.