Squirrel never nested.
The nest box had been ready and available for weeks but I don't think she ever entered it until her water broke and I placed her in it for the delivery. Then she was quite happy to stay there with the babies and never once tried to move them.
Be careful about leaving cabinets or drawers open. I friend left a dresser drawer open and her pregnant cat had her babies in it. My friend did not get her drawer back for a few weeks.