I think it has alot to do with how fit you are to start with. Probably 3-4 days maybe a week without riding if your really fit wont be noticed and is probably good for you. It worked for me when i was younger anyhow.

What i notice is that the older i get(60's) the less i can afford to sit around between riding if i want to maintain muscle tone and endurance, but my butt seems to be alright for a few weeks at a time.