Good point, that should have been "probably getting over the initial shock of entering the lack of sleep stage".

Babies end that stage, on average, at about 3 or 4 months. If they're still waking regularly in the night at 6 months then the parents are recommended to take additional measures to change that. Oh, and cuthbertcross's niece was sleeping through the night when she got back from the hospital (ie. day 3).