This can be tricky. If you are a winning player, it doesn't matter if you play for 4 hours or a 40 hour marathon. You're in it for the long haul anyway. You just have to feel it out. It might be good to have a plan in mind so you don't tilt your winnings away. If you've won a bunch and are way up... keep playing but as soon as you lose a hand or two, you might want to consider cashing out and taking a break from the table while you are ahead. I'm not a very good cash game player, so I don't know how valuable that advice is...