Well I don't know the proper answer. At first I dropped the block every time I shot. Lately I guess I don't do it often enough, about two or three times a year. I suppose you should do it when you feel the need. It is no doubt a good idea to look at it once in a while to make sure the firing pin is OK etc.
Right or wrong I drop the block out and give it a good cleaning after every time I shoot. I will before the year is out open the block so I can inspect the fireing pin and give that a good cleaning also.