What is best interval between masturbation for men?

No Set Time. There is no set interval that is best. The minimal time is whatever time it takes for an individual male to become erect again. There is no specific maximum time. Masturbation only becomes too frequent, when it begins to displace other activities or becomes a substitute for other non-sexual activities.
About 3 -4 days. You are doing it too frequently if your penis aches or feels sore.