I read that you can't book your shore excursions until 180 days and up to five days before departure, I plan on trying it this time for a few of the things I feel I MUST do and that way I can pay ahead of time I am hoping!
We are going on Carnival Glory 5/28. Once you have paid for your cruise (we paid ours off in March) and you have your booking no. you can book your excursions on Carnival's website. We have booked our 2 excursions already.
Keep in mind that once you book them they are immediately billed to your credit card, which can be a plus - our excursions are already paid for which leaves more money on our sign & sail card for other stuff. We have been advised by our travel agent to check in at the excursions desk when we get on the ship just to make sure all the excursion info is as it should be. Good idea - mistakes do happen.
When you are within 4 or 5 days from your cruise, you aren't able to booked excursions online. My husband and I found out the hard way. Once we got on the ship, we found out the excursion we wanted to do through Carnival was already booked! So if you want to do one, I would highly recommend booking online.