Some people claim this never happens---it has happened to us (unlucky?) 3 times. Barbados, flat tire on the bus--no spare! Panama, huge traffic jam, bus arrived 1 hour after ship due to depart. Freeport, boat from Dolphin Encounter pulled in 45 minutes after departure time!
In all three cases we were on Carnival tours, the tour directors were in touch with the ship and we boarded with no problems. It was worth every cent of the extra charge!!