Separate the wish from the commitment
Save the excursion you would enjoy, then label it optional until the operator confirms conditions and availability. Keep a version of the day that works without it. This approach does not predict cancellations; it reduces the consequences if plans change.
Do not chain assumptions
A boat arrival, transfer and international departure form separate commitments. Check each leg and its conditions. A line drawn on a map cannot confirm a timetable, and a short distance cannot guarantee a short journey.
Give the open day a purpose
Use it for the simplest version of the stay you wanted: a meal, time by the water or rest. If nothing changes, the buffer is still a holiday day. If a connection changes, it gives you choices.
