The only day you have a scheduled breakfast is the last morning of the cruise, and you can still eat at the buffet on that day, if you like. On the last day, you'll be scheduled to eat breakfast in the restaurant you had dinner in the night before at 6:30am for early seating and 7:45 for late. Again, the buffet is open, so you can go at your own pace.
On regular cruise days, breakfast is served at the buffet from about 7:30-10:30. There's also a buffet breakfast in Parrot Cay most mornings from about 8-10. Sitdown breakfast is usually in Lumière's/Triton's from 7:30-9:30.