As long as you are using them to book the reservation now and not depositing them to RCI for a future reservation, you should be ok. Dean will post a correction if I'm wrong. Someone in another thread posted that they called and were told the limit was 45 days, but I don't know for sure.
If you've found something that works, I would suggest booking it online through the
DVC RCI website now. If you don't, it may not be available later. The process takes about three days and you will be charged the $95 fee when you book. If there is a problem, DVC will call you and let you know.