I feed my baby for 20 mins each breast. And much sure she suckles. After that will play with her awhile before letting her slp again. If u repeat this cycle baby will know when is "feeding" time. U will also know there not enough milk when baby cries for more. For BF is takes a little more trial and error, because you do not know much milk ur breast produce exactly, and how much baby takes in exactly. So i go by timing.