Hrm, Can't say definitively. When I was younger (like, 15-17 or so) a close group of friends and I used to have pretty much weekly LAN parties on the weekend, we'd only go one night, but it generally consisted of us starting around 6 or 7 on a Friday night and still playing at 9 or 10 in the morning, when we started all getting so overtired that we couldn't really do much anymore, and were pretty much sitting around swapping music and stuff. To be honest, some of my fondest memories from that time in my life are from sitting through the night doing 4 on 4 CS matches, UT, Starcraft (my lord did we ever have some epic Starcraft matches). The admin abuse in CS would always result in someone getting pelted with empty Mountain Dew cans.
Although, come to think of it, the longest was my friend Nick and I spending a weekend with Diablo 2. We networked our PC's, started playing on a Friday, slept for a few hours Saturday, and continued through Saturday night til about noon on Sunday. Not uninterrupted, but still a hell of a session. The most memorable thing is the looting arguments we got in.
And no, I really don't regret any of those long sessions, although some of them carry bittersweet memories, as one of the friends who was most fun to play with has passed on. But I'm glad he and I got to spend that time doing something we both loved.
Sorry, sorta off topic.