Almost correct. They are't allowed to set it aside at all. They have to wait for break or lunch then they can purchase. Putting aside or holding back is what Walmart calls understocking. The employee can be fired for it.
This^^^^^ I know of a Wal-mart manager that was going through all of the Hot Wheels boxes. He would pick out all of the Treasure Hunt cars and sell them on Ebay. He got caught and lost his job.