On Halo 2 multiplayer, there was no pause. You press START, and it'll bring up a bunch of menus, but the game won't pause, and your character will still be able get hit.
It wasn't pausing for two reasons,
if one character paused in a game, every would have paused.
It would have been cheating to not get hit when paused. People could just go through a whole game in pause. They would still win.
The longest i ever had any system on was for 6 hours. The n64, and Mario Party 1 was on.
I do keep games on of when i eat, read, or when i can do something really quickly and come back. The TV gets turned off though.