Will masturbating frequently help you ejaculate more later during sex?

No. Just keeps your plumbing healthy and gives you a good time. But certainly use your hand pleasure to prepare yourself for the real event. Don't treat masterbation as a timed event, trying to get release quickly. That trains you equipment to do it when the real thing is there and you have no doubt heard of premature ejaculation and how it can be embarrassing--some guys even unload before they get inside! So enjoy masterbation, but take it slow and easy and learn to control your release so that you can wait a few minutes before unloading. Learning about your own body and how it responds is really important before you go sticking it somewhere else! Good luck and have fun.