The act may vary between the same couple from time to time. Partner specific differences are common. Ideally, anything above two minutes is considered superb. But these figures can be misleading. Place, availability of partner, surroundings, mental state etc determine the timings.
The term premature ejaculation is defined as the failure to maintain adequate erection and control the ejaculation till the time when both partners are sexually satisfied. The man has to get an adequate erection for penetration and maintain it till the partners are satisfied. The woman is the passive partner. Partner specific premature ejaculation is also reported.
To prolong the erection try the stop-start technique, the woman stops the stimulation of the penis just prior to the state of full excitement. Once the penis becomes flaccid, the stimulation is restarted. In the squeeze technique, just prior to the state of extreme excitement, the thumb and the fingers squeeze the base of the penis. This pressure acts as a noxious stimulus and hence ejaculation is delayed.