Welcome back to the Disney Parks Moms Panel, Kathleen!
You can't get anymore Disney than enjoying a meal at
Chef Mickey's Funtime Buffet! It was a must-do for almost every vacation when my children were younger.
The good news is the pricing is the same for the Breakfast (7:00am - 11:15am) as it is for the Brunch ( 11:30am - 2:30pm), you won't have to worry about paying a higher price if your bill comes back as a brunch buffet instead of a breakfast buffet. Plus, it will also be based off the time of your reservation, not when the restaurant is able to seat you, so you should be good-to-go for breakfast. One advantage of your 11:00am reservation is the additional items that will be added to the buffet after 11:30am for guests with brunch reservations; this turnover time will also mean fresher items available on the buffet line.
I hope this helps, Kathleen! I also hope this answer gets to you in time, I did not see an arrival date listed for your vacation on your question submission. Please let me know if I can be of any further assistance. I hope you have fun as you "Celebrate" with Mickey and the gang.
Faith