Pretty interesting topic, when I first started having sex like a lot of people I was so focused on lasting long enough, when nerves were no longer an issue and it could more or less go on for as long as I want...it depends. I too like a 20-30 session most of the times, but once or twice a week I like to have a nice long fuck that last a much longer time...I think its a lot like jerking off, sometimes you do it just to get off, sometimes you go a long time and enjoy it even more so.