3 month old baby only sleeps 20 mins?

You should remember that you are babysitting, if you watch him only during the day, maybe at night he will sleep more. Babies sleep on average 16 hours a day, but the longer he stays up during the day is better! I am sure he isnt getting any REM sleep, but as long as he isnt super cranky I am sure everything is ok. Maybe he is a night sleeper (super jealous lol)