Purely empirical... just figuring out what I did last day/evening, and then noticed how sleep is affected in certain patterns.

It didn't take me months to figure it out (not OP), you might get some insights quickly. Get one of the fitness trackers(Fitbit/MiBand/apple watch) and wear the watch for a week, then take a note of the things you're doing in the evenings and see how if affects your baseline from the previous week. For me, exercise was a clear winner on the first day - I spend less time awake in bed, sleep longer and higher quality _every_ day I exercise. Others, like working late, or playing video games late took longer to figure out.