How long should a man make on a woman so he can be certain he has totally ejaculated in the woman so she can get pregnant?

Same question, same answer: You should plan your encounter during the time of the month when she is ovulating. Regarding how much time, it all depends on you... some men take more time, some take less. The most important thing is that you finish what you've started.

Ejaculation can be felt and then the penis becomes less hard. Having sex during her fertile period will help.