Because you are feeding on demand you may not notice a HUGE reaction when your milk does come in. No, 4 days isn't too long, it's usually 3-7 days... However long it takes for the progesterone level to decrease enuogh to let the prolactin take over and make milk.
No he will probably feed just as often in the beginning. For the next 4 to six weeks baby will go through several growth spurts, so many that it might seem like one long one

. hang in there, sleep when baby sleeps, and know that in a months time baby will have made a routine and might eat only every 2-4 hours between naps.
You're doing great!
