Can you increase the time?

yes what you need to practice is the start and stop methode.

start masturbating until just about when you feel you are going to ejculate then STOP. let the feeling subside a little then start again. repeate as many times as possible untile you can not take it any more and have to ejaculate. thiss will not only  allow you to last longer but also increase the amount of semen that you ejaculate. especially if you drink a lot of water.