I think valet services are available 24 hours a day. I know when we arrived at BWV at 1 am one trip, there was a valet available to unload the trunk and park the car. He also ended up delivering the luggage to our room (and refused a second tip for this service), so there may have been a period of time when no one was available at the desk out front. I have called for my car before 5 am a couple of times (to take DD to the airport for a pre-7 am flight home) and always had prompt and efficient service.
Ralph