Back when I used to shoot my 22's regularly, I joked that I cleaned them evey February 29th, rather they needed it or not. If I happened to forget, I'd just wait until next time.
In truth, I probably cleaned them "every so often." No set schedule. For example I might go all hunting season and not clean the rifle I squirrel hunted with, but I might not shoot that two or three times a trip. I might clean a Ruger Standard after every trip to the range, but that trip might be several hundred rounds.