I was thinking after 4-8 hours but then that's usually when I take a nap or pass out so that's not it.. Pretty awake near the end of the day though but not past that so 8-12 for sure.

Very interesting. It seems most people are like myself and more 'active' 8-12 hours in. I wonder if it's something I've unconsciously trained myself for since I would talk or play games with people who had jobs or school and that was when they were available. Although, on the other hand I remember being very sleepy in school so maybe I've just been this way forever.