Hi! when you book your shore excursions with the cruise ship you are guaranteed that the ship will not sail off without you if your excursion returns late!!!!
I have done both, excursions with the ship and independent excursions - the independent shore excursions if I use them I make sure we are at the port for at least 8 hrs or longer - and our excursions is no longer than 3 hrs - 4 hrs at the most. That way if the bus/car etc... from your independent company breaks down etc... you still have enough time to get back to Port on your own by taxi etc... Make sure your independent excursion leaves early morning which gives you the afternoon if anything happens.
I have seen a many people waive to the ship as we leave port! It's not funny! First they are fined $200 - $300, then they need to find a hotel, pay for their diner and brekky, get a flight to the next destination = very expensive!
It's Cruising Time....