You may book the Poly (and any other resort in the Disney Collection) 11 months prior to desired check out.
Keep in mind that if you cancel the reservation, the points cannot then be used to make a reservation at a
DVC resort or for an exchange via II (World Passport Collection). So unless you have reason to believe the Poly will sell out for your dates a long way in advance, there's no reason to be in a big hurry to make the reservation.
Best wishes -