This is not all that different from a land based resort program.

In the busier times of the year space, like in any popular resort hotel, can be at a premium. Overall your timing will mostly be based on the overall size of your program. Larger programs that require similar sized staterooms and stateroom categories will benefit from booking further out. The earlier you book the better the pricing tends to be as well. As a final thought the greater the flexibility you have in the dates of your program the more options you will have in deciding when to book.