Booking it early not only gives you better pricing, but buying it within 10 days of the original booking also allows for pre-existing conditions.
If you flip a cruise, the insurance company still goes by the date that the original deposit was put down. Flipping it does not give you a newer booking date. And if you had booked it outside of Disney on the original cruise, you can no longer flip the insurance too. Believe me, I've been on the merry-go-round about this in the past. For us, pre-existing conditions are vital. We can't book any insurance now that will include that once we flip the current cruise to 2014.