How long can you sit and play a game before you have to take a break (whether it's stopping to go to the bathroom, giving your eyes a break, or just stopping to go to sleep)?
For me, it depends on when the last time I've done three things. If I've had plenty of sleep the night before, I've eaten recently and I've been to the bathroom recently, then I can go for quite a while. Four or five hours, provided the game is interesting enough.
It all depends really. For singleplayer it would be an hour or two whereas if I'm playing a fun game online with friends such as GTA V I can sit and wait for around 4-5 hours (toilet break if I need to)