I called Grosvenor and just asked for the room rates of the dates I was staying, then after they gave me those I told them I had the Entertainment book and asked what that rate was. I was quoted $55 a night for the 1st week in May. I made the reservation and the cancellation policy is either 48 hours or 72 hours before arrival date, can't remember which. I WILL be cancelling though because we got rooms at Old Key West instead.
If you want an Ent. book rate, I would call quickly, they only have so many rooms at that rate and you might end up getting 1/2 your nights at that rate and 1/2 at regular rate, especially if you are staying over a weekend.