It is impossible to say unequivocally, there is a state in which it is good to win, you need to look at this first of all not in terms of time, but under what conditions you can show your a-game and win.
I am able to play anytime pretty much (retired) but have found it more difficult to cash (MTTs) on the weekends - seems to be more variance happening with both losing races and taking beats ending most tourneys for me. And this is across 4 different sites I play on. Perhaps more players on weekend and greater chasing going on.
I think there are no days but good times, which can be any day depending on the person.
But without a doubt, the weekends are when the best tournaments are