When a US Navy destroyer ship is underway for two months (work hours/schedule)?

When a US Navy destroyer ship is underway for two months ... how hectic is the work schedule for first-year Division Officers (O-1 ensigns)? I know it depends on the mission, but let's ume that they are not in an actual combat zone. How many hours a week do they actually work on average when underway? Can they actually take a complete day or two off each week? How about when they are in ports? As a civilian, I am very curious ...