Depends, 1st are you
DVC members? if so, is WL your home resort? if yes to all these ? then at your 11 month window. Christmas time is extreamly busy at WDW and rooms go fast. If your home resort is other than WL then at the 7 month window. If you are paying cash, then right now is good or soon after the 1st of the year. Or you can look into renting points from another member ( see rental board).