That chance is why we try to fly in the night before. That way changes or flight delays won't ruin a cruise. If the airline changes a flight schedule, you can typically call them and the will move your flight without charging you.
AA chagned our flight time for next month, but since they changed it so we leave earlier, I don't care. Otherwie we would be looking for a hotel room and having them fly us out the day before.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007