The lag
The difference between 23:59 and 00:01 is two minutes, pretty minor. On some occasions, though, it can throw you off pretty significantly.
I have some unpublished drafts in my posts — something like a collection of notes that I take when the idea strikes, so that I can finish it later.
Just now when I wanted to write another blog post I got dizzy for a couple minutes: a whole day disappeared from my backlog.

Sounds pretty obvious and at any other occasion I wouldn't notice it. But for some reason tonight it threw me off for good, it was almost surreal.
Felt a bit like a jet lag with the jet (or any real lag, really).