I think it completely depends on so many things. Who with. The situation etc. it can be a quickie. Or it can be made to last hours. ?
The longer the better. I agree with a lot of people here it depends on when and where. Weekday mornings are quickies as we both have to get to work. Evenings and weekends however go on much much longer.
The singer Sting once claimed he could make it last eight hours, but later added that this time included dinner and a film.
It depends upon whether or not it's a quickie, a longie, or a mediumie.
The longie lasts loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong.