It's overnight for me, but I'm ultra-rapid cycling, so it makes sense that the changes are very sudden.

There's no real pattern other than stress making me decompensate and meds improving things. I'm not really sure how to identify 'level', since I usually only notice I'm hypomanic looking back.

I can tell when I'm depressed or mixed because the feelings are so overwhelming and negative. I think there's a fine line between happy and hypomanic, though, and that one is definitely harder to notice.

I would suggest that you not spend too much time obsessing over your moods and diagnosis, because this adds a lot of stress and I find that when I spend too much time thinking about bipolar disorder it really depresses me. You could maybe set aside a few times each day to do 'mood checks' where you spend a few minutes considering what mood you're in, then maybe record it in a mood journal and move on to something else. Obsessing over it all can really interfere with living as normal a life as possible.