Yes, it's common for them to hide for a few days after they molt. During this time, their new exoskeleton is really soft, and they have little to no protection from predators or the environment. Hiding allows their exoskeleton some time to harden.
The exoskeleton looks almost like a replica of their body. It all depends mine molted about every two weeks when they were younger but, lately it's been more like every 4-6 weeks.
Understand, that there is a chance that he'll never come out...Sometimes, they're perfectly happy living in the rocks..I've got a blood shrimp that stays in the rocks, the only way I can see him is to look under the rock and see his whiskers.