Besides my actually rounds when I am timing myself for like an amatuer fight or more, I find shadow boxing addicting. For example if I am at work and I go take a bathroom break or something and I look in the mirrior to wash my hands I end up throwing some punches or something for a minute or two. But like I said it becomes addicting.

But basically to answer your questions I just do about two more rounds than an actual regulated amatuer fight would be that way I will always be ready. Train yourself harder than you actually need to for the fight so you will always be ready.