Depends too on how many hours are on it.
It it new or an old ****ebox?
Personally I find 20 hours quite an amazingly large figure (I'm not saying I don't agree with it though).
So for every 10 hours, 2 hours more are required for maintenance minimum!
Better than the stealth bombers and some other military types etc, they can require 100 hours or more maintenance for every hour in the air!