We did Palos on the Grand Cayman night for about the same reason (you have to be back on the boat at 4:30). Also it was our first cruise and according to the rotations, the 4th night is in the same restaurant as the 1st and the last night. So we figured we would have two nights in each restaurant this way. We had the APLAPLA rotation, so we missed the second 'A' dinner.
Incidentally, Palo's is a long dinner. We must have been there 3 hours, which caused us to miss some of the family events that the kids wanted us to go to (i.e. scavenger hunt) Oh well, next time!