Hmmm, good question! I'm super curious to see what others say. Because I have had my birds for 2 months and not really switched their toys out. I did get a few new and add them but they really like their toys so I haven't wanted to take them. AND it took them forever to warm up to playing with toys in the first place. That being said I do switch them around occasionally.
I think it depends on your bird's personality. Some birds are bold and very curious and like to have new things to explore so they don't get bored, and I guess for those birds it's good to switch things around quite often. My little Buddy is quite a timid bird, he doesn't like change and he's very wary of anything new - if I buy a new toy for him the toy has to do "introduction time" at some distance outside the cage until he decides it's not a scary monster, and then gradually I bring it closer until he's happy to investigate it in his own time without getting frightened. So for Buddy, I change out only one of his toys each week, and I always leave his current favourite in the cage because I think that keeps him happy when I'm not at home, kind of like a toddler's security blanket (At the moment his favourite is a spinning wheel with little roller balls inside & he loves to lift up his foot and give the wheel a good spin, which is very cute , I wish I could catch it on camera!)
I can tell when my birds are starting to get bored with a particular toy and that is when I switch. If I'm in the mood for a big cage renovation I will swap everything and perches, but sometimes I just swap that one toy and switch the locations of others. My budgies have favorite places they like to play so that gets taken into account, too.
So, I don't have a set amount of time, really. I take the cues from the budgies. Yazzi is more curious and gets bored quicker whereas Piccolo takes a bit to warm up.
I just switch toys around every time I do a big cage clean (which is once a week). For daily cleaning, I usually just leave everything how it is as Mallorn prefers I don't touch her toys unless the new configuration is better, so I need a bit to figure out how to appeal to her delicate interests
and Princess Mallorn!
Thank you to Deb for her wonderful Faery magic
I switch out their toys once a week which is also when I do a deep cleaning of their cage. I find that my birds tend to get bored rather fast to be honest. After a few days you can tell that they're getting bored of their toy. One thing I found that helps is actually having lots of shreddable toys rather that hardwood toys. They do not play with the hardwood toys much really... My birds also seem to really like toys that have bells and ones that are plastic. I change the perches every two weeks.