You can book rewards stays at Marriott up to a year in advance - so my advice is the sooner you try to book, the better - especially for the more touristy spots. I understand from a colleague trying to go to hawaii with Marriott rewards that they had to book almost one year ahead of time to get a spot. We recently redeemed points for a hotel to take the kid to Disney World for next April and already a few of the Marriott hotels had no rooms available for that far ahead. Good luck.