With my home defense guns that don't get carried, I'll let that ammo go for years, because it doesn't get carried. It's fine.
For carry ammo, lately it kinda depends on what I get into. I carry IWB and if I sweat through my cloths heavily, get rained on and soaked, or similar, that ammo comes out right away and new stuff goes in.
Generally I'll unload my carry gun a couple times per week and dry fire with snap caps. The round that's chambered and ejected over and over gets chewed up a bit, and I'll rotate that down into the mag and bring up a fresh one from time to time.
We're coming into shore fishing season soon where I live and the fishing ammo will get cycled out a but more quickly. I'll sweat, get rained on, get splashed, its a more corrosive environment, etc. If you saw where I fish, you'd carry too.
Ammo that gets cycled out goes into a box and then eventually gets shot up on a range day.