We waited about 20 minutes this past Saturday (over Memorial Weekend), but later in the day, the wait was about 5 minutes. It's a cute ride, but I wouldn't wait in line more than 15-20 minutes for it. Grab a fast pass for Soarin' first and then head over to Monsters.
Also, you must see the Aladdin show - it was awesome - my dh and ds10 were abit hesitant about going to Aladdin but they LOVED it!!!!!!!!!!!!