I would say, if you are going full time for your senior year as an undergrad, it depends on your major, (joker is right, commitments for sure), credit hours, aspirations (if you wanna go to graduate school, get your GRE/GMAT/MCAT/LSAT etc. over with now and start applying), career options (network with your professors hardcore), ignore your social life: put all your friends on hold :p there's no room for them if you wanna sleep.

Just replace "Social Life" with "Video Games". Basically, it'll cut into your sleep or grades either way. So I'd say 1 hour, maybe, per day.