I am in two campaigns that run in the 3 or less to 4 hour mark. A Saturday morning game played online with a group that includes players in Qatar and Taiwan, so the time differential means we can only play for about 3 hours. I am also in a Friday night game in which some players can't arrive before 7:30, so we usually run until about 11, though we've run until 1 a couple of times.
I am in one campaign that runs right around a 4 hour time slot twice a month on Saturday afternoons.
I run a campaign that meets about twice a month for 6-12 hour sessions. We generally eat lunch together and hang out, so the game starts around 12:30 or 1, we take an hour or so break for dinner, and we'll finish around 8 most days. We'll end earlier or start later if someone has plans, and we've run to or past midnight on at least three occasions that I can recall, always related to a climax of a plot arc.