Moving Dummy Dates

[MedicGoofy]

Just wondering, how far forward, or how often can you move a dummy date before DCL says, wait....book it or lose it? I have a couple of cruises I know I will be taking in the next couple of years, probably into 2015 BUT, then my family wants to take a big family cruise several years later when my neice is a little older. Im curious as to how long you can hold onto a dummy date and move it around?

Anyone have any experience with shuffling one around?

Thanks