Perhaps there should be examination questions on how to fill in your log book ? Before reading some of the questions that get raised here, I never thought it was that difficult. The times start when you first move under your own steam. The time stops when you arrive on stand and shut the engines down. The total time was the latter minus the former, unless you had swapped duties with someone else in between, or had died en-route.
If you are in command of the flight you are P1. If you are the co-pilot carrying out co-pilot duties you are P2. If you are co-pilot acting as the pilot in command and under their supervision you are P1/S. If you are sitting on the jump seat you are supernumery and needn't bother logging it at all.
Day hours were about 30 minutes before the sun came up, until 30 minutes after the sun went down, unless weather conditions or some other valid consideration made you judge otherwise. Night hours were the rest of the time. Instrument flying was when you (manually or through the auto flight system) were flying with sole reference to instruments (in airliners virtually the entire time you are aloft).
If you are still not sure then apply a bit of common sense and judgement. Nobody will fault you for that.