The buffet is basically the ship's living room
Before your cabin is even ready on embarkation day, the buffet is almost always the first place open, and it stays that way as the go-to option for the rest of the week. It's fully included in your fare, no per-plate charge, no surprise bill, which is part of why it becomes the default even for people who planned to eat every meal in the main dining room.
When it's actually open
Most ships start breakfast service between 6:30 and 7:00 a.m., sometimes earlier on port days with early excursions, and keep dinner running until roughly 9:00 or 9:30 p.m. After that, a smaller grab-and-go spread or limited late-night menu usually takes over rather than the full hot buffet. The exact times shift a little by ship and itinerary, so it's worth a quick glance at the daily planner in your cabin or the cruise line's app the night before, don't assume every ship runs the same schedule.
Timing your visit to skip the crowds
The buffet gets genuinely packed twice a day: right at opening, and again around 7:00-8:00 p.m. If you can eat 20-30 minutes off either of those windows, you'll usually walk into shorter lines and find a table without circling the room. It sounds like a small trick, but it makes a real difference on a full ship.
How it compares to the main dining room
It's less about which one is "better" and more about pace. The main dining room gives you a plated, multi-course meal with table service, a slower, more polished evening. The buffet trades some of that polish for speed and self-service variety, which is exactly why it works so well for big families or picky eaters: everyone can build their own plate instead of agreeing on one shared menu.
A few practical notes
You can generally take a reasonable amount of food back to your cabin, though if you want a full meal there, ordering actual room service tends to travel and hold up better. And no, you won't need a reservation, the buffet is walk-in only, which is exactly why it fills the gaps when everything else requires advance planning.