Is it legal if charged a transfer fee within the same complex if lease starts Aug. 1st but cannot move in until a week into the month anyway?

My college student daughter is upgrading to a 2 bedroom apartment in an off-campus complex which mostly caters to college students. The move out day for the bulk of the students is July 31st. Her new lease starts Aug. 1st. The company is charging her and her roommate an extra $500 transfer fee to have their new apartment ready sometime in the first week of August. If they do not pay the $500, they have to completely move out on the 31st and will not be able to move in to the new place until the 17th of Aug. If they are paying a full month's rent, is this legal? This fee is not in the lease.