How to reduce time of "cumming" while having sex?

Sex: Perhaps ejaculating less frequently. Otherwise not sure what you are really asking.

Premature ejaculate: There are ways to increase duration of sex before ejaculating. You could masturbate, so that the second time you will go longer, you could use a topical anesthetic cream or lotion to reduce sensation, you could engage in mutual oral sex first and have results similar to masturbation, or try and train yourself to think of other things (superbowl?) while having intercourse to slow yourself down.