The ship rarely if ever will change the Ship's time. They plan all events by Ship's time, and excursions, and ESPECIALLY arrivals/departures. KEEP YOUR WATCHES ON SHIP'S TIME! Also find out the time difference between the ship and land.
They will only change the time if the cruise is a long repositioning cruise (IE Miami-los angeles, we changed ship's time as we went west) or daylight saving's time changes.