It seems like they run the waitlist at certain times of the day. We have had waitlist for a room. Happened to check myself and saw the room available, so I booked it myself and cancelled reservations.
I have also needed to hold a room, call MS and have them book it. I would hold it (start booking), when agent was ready, I would cancel the booking. They would refresh and immediately grab.
For that reason, I agree it is realtime.