Santorini does not have a conventional cruise terminal where large cruise ships can dock directly. Instead, cruise ships generally anchor offshore, and passengers are transported to the island by smaller boats known as tenders.
Depending on the number of ships visiting, tender arrangements, passenger disembarkation procedures, and local transportation capacity, reaching the island can take considerably longer than expected.
In our experience, there was a five-hour difference between the ship's arrival and the time we were finally able to go ashore.

This was an important lesson for us: the scheduled arrival time does not necessarily mean you can start exploring immediately.