Some of you people are crazy!!
For me, probably the most is about 7 hours. That was quite a few years ago.
Nowadays, I just don't have much time to spend on playing games. Not to mention that there also aren't that many good titles out right now. So my interest has lowered.
When a good game does come out, I do try to make sure that I spend time playing it and finishing it as well. Just not all in one sitting tough