HOW LONG DO MY GUESTS HAVE TO BOOK ROOMS?
More often than not, the block comes with a one-month cutoff prior to check-in. Once that cutoff date arrives, the discounted group rate is no longer available and any rooms that were not reserved are released back to the hotel so they can try to sell the rooms. At that point the guests will need to book at the current hotel rate.
One way to combat this is to book a few rooms under the event host's name and then change the reservation name if a guest forgot to book. Just be sure to cancel unused rooms by the hotel's cancellation deadline.