If the materials are unfinished, then they will acclimatize quickly (~1 week). The neck will ship with minimal tension on the truss rod. It won't be rattling around.

The truth is that wood will continue to move for about a year. There's nothing to be done about that except rely on the manufacturer's quality control and return policy. It's best not to do attempt any fret leveling until you've had the instrument in playing condition for awhile.