How many times masturbuting can be done in a day?

As many as you want. Just know your own limits; if you feel tired after or during it, you have had enough, wait until you feel ready before starting again. If your arm aches, you have had enough, wait until you feel ready before starting again. The same for if your penis starts to hurt, or you feel a bit light headed, etc. Just be reasonable and space it out over the day.