We booked a 2BR last August at SSR and did so in March (which is 5 months out). Late August is probably easier (many kids are back to school). OKW and SSR are the 2 largest resorts so I'd guess you wouldn't have a problem. When do you think you'll be in the
DVC system and able to make reservations? I know the time line is longer on a resale than through Disney. If it's within a month to 6 weeks, you should be OK.