You have to do this within your 180 day window. But you want to do it right on your 180 day if possible. It really is that popular. Especially if F. goes back to twice weekly.
It is available for lunch or dinner at : Mama Melrose, Hollywood and Vine (1 TS credit on the
DDP) and Brown Derby (2 TS credits). If paying OOP it is a fixed price for the entire meal which includes the full buffet and beverage at H&V or an appy, entree, dessert, and beverage at the other 2. You order from the regular menu, but pay the package's fixed price. At the end of the meal you are given vouchers for the number of people on the reservation.
Make sure you are making the reservation for the F. Package, and not a regular restaurant reservation. If you are not asked for a credit card number to guarantee it, then you have made the wrong type of res. If you do not cancel and fail to show up, you will be charged a cancellation fee.
If you look under the dining tab at the top of the page you can find more info on the F. package, including prices for each meal (which includes a price range to account for holiday surcharges).