How many days after delivery does your breast milk kicks in ?During this period, baby feed FM first?

How many days after delivery does your breast milk kicks in ? During this period, baby feed FM first ? I'm in the hospital now on my 3rd day, I don't see any milk coming out and the lactation nurse really squeeze the nipples for the massage before latching. She asked me to squeeze real hard to stimulate, I didn't know about this and it seems too late... feeling so sad n lost....