These days, my DnD sessions last about 2 to 3 hours and I'm ecstatic about that.
Before my sabbatical from playing, our average saturday night sessions were about 6-8 hours, which I'm going to guess is fairly typical.
But back in college, we'd play from the lat afternoon until the wee hours of the morning. And sometimes do the same the next day.
I have a great deal of nostalgia for those sessions, but in reality we probably got only a few hours of real gaming in.
We bullcrapped, argued, joked, ate and laughed far more than we played.
And that was fine. That's the way a bunch of guys from the ages of 18 to 22 should spend their time.
Most of us were a little socially awkward (shocking, I know) in one way or another. In my case, I was very focused on getting my Graphic Design degree within 4 years of a 5 year program and was pretty shy around girls.
But all of us were "dorks" and "geeks" and we became friends and shared our interests with each other. And that's what this hobby is really all about.