I pretty much clean mine every time I shoot it because it usually ends up back in my safe till.... whenever. If you shoot it often enough, I guess you could wait till after ?so many? shootings. Make sure you get the gas tube etc.
that's pretty much up to you the user. everyone is different on how they vew maintenance of their own tools. you can't go wrong if you get in the habit of cleaning after every shooting session. at least you'll know that they are ready to go any time you might need them. and, if you can't get to them for a while, at least they are cleaned and lubed to protect against corrosion or rust.
i guess it kind of like, are you one of those that wipes off your tools after you are done using them, or washes after going to the bathroom, etc. it's preventative maintenance and protecting your investments.