I don't think I have hit 4 hours straight, but definitely at least 2 hours straight. I love to light the candles, put on some music, and fuck all night. It feels so good. I'm not sure if there is a 4 hour limit, but maybe I will find out.
When I go over an hour or 2 with intercourse, I usually need to bust a nut or two and go flaccid for 5-10 minutes and get some water. I think 3 hours is the longest I have gone during sex but I went flaccid for a bit.