Dr Jack Newman - Breastfeeding Help and Lactaion Consultant Training  
Good Drinking
Note the position of the baby at the breast. Chin in the breast, nose not touching, baby’s lower lip covering more of the areola with the lower lip than the upper. An asymmetric latch.

The pause in the chin as the baby sucks means the baby just got a mouth full of milk. The longer the pause, the more milk he got.

A baby who drinks like this for 20 minutes straight (for example, we are not recommending feeding by the clock), might not take the other side, he would be full.

Timing feedings makes no sense.