We booked them at about a week past our 180 mark so I'm not sure if its +10 or not. As others have noted it is not needed unless going at peak times over the holidays. I like the piece of mind that it's done. We can always modify as we get closer. We did book the Luau at nearly 180 because we wanted the VIP for my mother in laws birthday and read that better seating could depend on how early you book. I'm not sure this is true, but it's done and I dont have to speculate.
Additionally, I just reserved cabanas for two of our days and will decide if we want to keep two or drop one. They will fill up quickly as we get closer as the pool construction (early October for our trip) may limit chairs and cabana numbers.
Mike