Newborn Baby Care: Waking Baby to Eat
In my opinion, it is best to let babies sleep when they are sleepy and eat when they are hungry. Allowing babies to follow their own schedule helps to set good patterns for how they regulate their food intake. By allowing your baby to eat only when he is hungry, you will be helping him establish good eating habits for the rest of his life.
Of course, this works best if your and your baby's schedules are basically the same, especially at night. If your baby is keeping you up at night, it might work better to set a feeding schedule that works for you. Expect your baby to adjust to any change in routine over about a three-week period.
However, if you're just beginning to nurse your baby, you should wake the baby about every three hours to nurse over the first few weeks, in order to ensure an adequate supply of milk.