If it's really good then about 10 minutes. My saving grace is that I am ready to go again within a minute or two. I orgasm quickly, but I recover very quickly too. It's not uncommon for me to cum many times in a session. What usually gets me is when she cums, sometimes it just feels so good that I lose it.
I can't understand how guys last for 45 minutes or more. Does the woman not cum at all? I suppose I could if I really took my time and stayed with slow strokes, or pulled out for a second or two when I got close, but where's the fun in that? Start slow, finish hard, cum like a maniac together usually, then start it over again. That's great sex for me, marathon sessions with no climax just seem lame.