We just sailed from Vancouver to Hawaii with the first 5 days at sea. They would announce and print in the Capers on which nights we needed to adjust our clocks. We then arrived in our first port on Hawaii time.
It is up to the ship's discretion, they can do whatever they think is best. Most ships try to stay with whatever time zone they are in, and change at midnight. But that is not an ironclad rule. Many ships going to the Western Caribbean from Florida never roll their clocks back to central time. They just basically allow you to think that the local time is an hour later than it really is. I don't know how they can get away with this, but they do.