The pp is correct that the DDP must be added no later than 72 hours (3 days) prior to arrival, but if you currently have a room only reservation, I think the room only has to be cancelled/refunded and an AP ticketless package booked. If AP bookings work the same as regular bookings (which I think they do), adding the DDP to an AP room makes it a package and follows the same deposit/cancellation guidelines as non-AP bookings (i.e., packages require a deposit of $200, with balance due 45 days prior to arrival; room only ressies require 1 night room rate + tax, with balance due at check in).