2-3 Hours penetrative sex would be horrible. First and foremost the woman would start to hurt, and the guy would get very tired. 2-3 hours of "sexual contact" is more believable. Including foreplay and oral sex and whatnot, but 3 hours of raw sex would not be that fun.
Usually me and my girlfriend spend around half an hour kissing/touching, half an hour giving oral or whatnot, depending on our moods. And average around 45 minutes of sex followed by the cuddling :3
That's just averages though.
Another thing, if a guy is just pumping away and thinking of something else to prolong the sex and delay orgasm, he's not going to enjoy himself. Why not stop and pleasure the lady if you want the whole experience to last longer. It's what I do and it works perfectly.