I'd say depending on how much your baby weighed at birth and how well she is eating thoughout the rest of the day. if she's awake and active(as active as a newborn is!)at times throughout the dayand pees and poops plenty I'd say let her sleep. Why not? Thank God newborns know they have to eat! They are not going to sleep until they starve!!! Of course a premature baby or one with jaundice will need to be woke up to nurse. But if your baby is full term and healthy I'd say lucky girl enjoy the sleep. but don't get used to it. The minute you brag about it they'll start getting up evey half hour!