I don't know yet. I just got my first canister in mid/late January. I checked it after a couple weeks and again at one month (February). So far, I haven't had to do any cleaning. I'm going to check it again either tonight or tomorrow, depending on how much energy I have left tonight. I've been sick this week and am getting a CT scan for my sinuses today. Woohoo.
Anyway, my tank is technically stocked, since I've got the fish that I will have in there for now, but they are all young so currently it's understocked. Get my meaning? They are all smaller, so they don't put the full bioload they will once they are older. I planned for the future, so to speak. Sorry, rambling again.
Anyway, I'm projecting that I'll only have to do a cleaning every couple months. I'll probably only clean part of it at a time, though, to prevent a mini cycle since most of my canister is bio media.