Most probably, we’ll be on time and at a place. And we do our best to be precise: thoroughly prepare the boat, and design the stages so that if we have long crossings we always include some extra time to wait for good weather.
But it still sometimes happens due to weather conditions, or need of urgent repairs.
All in all, even if the changes happen, we usually can make the trip fit the same dates, but slightly different pick-up or drop-off places(say, on the next island to a planned one). Of course, we’ll anyway do it at a most convenient place close to the airport.