They are cached for 30 min right now:
https://github.com/itchio/butler/blob/05bdf572443296d9da9f63d458c72f829d19c883/d...
I wouldn't expect the app to break if a collection disappears though, I'll definitely have to test for that.
I think, for me, new collections that I added were added in about 30min. The cached, but non-functioning collection I deleted persisted for longer than that, however.
