I don't really remember for sure but I think we booked it day of the reservation. My husband thinks we booked it and then changed our minds but we can't really remember. Whichever way we did it, it wasn't a big deal for our cruise. We booked it for the day we were in Cabo. You might have more people staying on board on Christmas day as I would imagine lots of places would be closed in port that day. Hope you enjoy it!