My 15 week old DS's patterns differ. It is usually 2-3 hours feeding (Both BF/Formula) and every 4-6 hours overnight. One night he fed every 2 hours at 14 weeks and yesterday I was away from him and his feeds were breast, 180ml formula, breast, 120ml formula every two hours. Sometimes he can drain my breast in 5 minutes other times 10-15 minutes. Babies know when they're full and may take themselves off breast/fall asleep. If he wasnt satisfied then he'd let you know, 6-8 full (pale yellow) napkins will let you know he is getting enough. I noticed my DS's napkins weren't as full when my supply was low.