There is no should. I usually hear 1-2 times a day from guys. It's not like it's going to hurt you. Although you might want to switch up your technique from time to time.
As often as you feel the need and can find the privacy. Some guys are a few times a day and some are once every few weeks. You have to find the normal rhythm of your body and go with that.
Every guy/girl is different. One of my guy friends actually said 8 times a day was normal for them! I don't think MOST guys masturbate that often but I definitely hear anywhere from a couple times a week or few times a day. Some guys don't masturbate much at all even.