I used to spend hours on cleaning and rearranging. I can't do it any more! I change perches around twice a month. The toys I try to change around once a week. I usually put in 1 toy they haven't seen for a while and swap 2 from the other cage. That gives them each 3 "new" toys a week. There are times where I get lazy and just rotate them around in the cage without swapping them.
And my only rule is that as long as the toy is out of "damage zone" (can't be pooped on) it's good.