Somewhere around 12 hours.
We started around 8 at night, and ended at 8 in the morning when my mother got up to exercise and go to work.
It was with my one brother and a friend on the Game Cube with like 3 different games. I can't remember exactly as that was at least 4 years ago, but I do know we played like 1 James Bond game, and a fighting game along with one other game.