Actual intercourse (penis in vagina, and fucking) probably averages about 5-10 minutes for me. The longest I've ever gone is about 35 minutes, and the women in those cases were looking for me to finish up, and they were getting tired and sore.
That said, foreplay can be anywhere from 1 minute to 10-20 minutes. When your woman says she wants your penis deep inside her right now, I tend to obey! Only 2 of the 10 women I've been with could cum from intercourse, and my wife is not one of them. So we use other techniques, and sometimes toys, to ensure she has an orgasm every time.