Hehe yes yes Super/Kid Buu have fallen asleep in the short pauses between battles, at most a Majin needs a few minutes to be fully rested.

If your going by Dragon Ball Super, Buu according to Mr. Satan, only needs one second to sleep to be fully rested, rarely ending up sleeping for a month or two at a time.

Going by Super's logic, I'd suppose a full ten minute rest per day would be more than enough for a Majin to be fully rested without worry of suddenly falling into a two month long slumber.