The best time to create those cute posed portraits of your just born babies would be between 5 and 15 days after birth.
Why 5 - 15 days - because it takes about a week for the baby and the mother to come back home and settle into a routine, post which we can gauge their sleep-awake pattern and schedule the photoshoot session accordingly.
The first two weeks the baby still likes to be curled up and remain in the womb position, they like to be kept warm and their bones are still very flexible. So, it becomes easy to wrap them up and pose them in different ways, of course keeping safety as the first priority. (Hence please get these done with only a professional newborn photographer and not try these at home on your own).
Newborn Photoshoot by Soumita