hi! basically, if baby is hungry(newborn), there are some clues you will aware,
first, he/she will look around and open his /her mouth and search the nipple.
then , he/she will suck his/her finger into his/her mouth.
last, if he/she still cannot be satified, he/she will cry heavily and let you know that he/she is hungry.
besides hunger, baby will cry because of flwg other reasons:
1) diaper wet
2) too hot or too cold.
3) sleepy.
or other reasons .
but for breastfed babies, you should feed him base on his demand, not schedule, if you see his above 3 clues, he is hungry and you should feed him immediatly, basically for new born, he will need breastmilk 12-14 times per day, and each will need feeding time at least 20 mins to 45 mins.