When you book your cruise, you will need to choose a dining time. This will be the time you are allowed to eat in the main dining room. If you miss your assigned dining time, you cannot join another dining time. You will need to eat at a specialty restaurant, or at the buffet. You definitely do not want to miss dinner in the main dining room though. 

Assigned Dining

You may choose between early seating which you must go to the dining room at 5:30pm, or late seating which you must go to the dining room at 7:45pm. If you choose assigned dining, you need to be to the dining room at your assigned time within a 10 minute window. You will be assigned the same table every night and will likely sit with strangers. You will also have the same wait staff each night. The assigned dining room is typically the aft dining room.

Anytime Dining

This concept is the same as a land based restaurant. You can show up any time between 5:30pm and 9:00pm to eat, whenever you get hungry. You can still have the same wait staff each night if you want them, you can still sit with strangers if you wish or you can sit with just your family. You can also have dinner with your friends one night if you wish, as long as they have anytime dining as well. The anytime dining room is typically the fwd dining room.