Hi Carol:
Congratulations on your
Chef Mickey's Advance Dining Reservation. My family loves a breakfast at Chef Mickey's, where we enjoy a huge breakfast buffet (including eggs, waffles, pastries, cereals, and more). The energy at Chef Mickey's is incredible. My boys not only enjoy the huge buffet, but their smiles shine when Mickey, Donald, Goofy, Pluto, and Minnie stop by the table to pose for pictures and sign autographs.
I would say a comfortable breakfast at Chef Mickey's takes about 45 minutes or so, maybe 60 if you linger. Of course, timing can vary depending on a number of factors, but since Chef Mickey's is a buffet, you have some control over how long the meal takes. If you need a short meal, inform your server. If possible, your server may be able to help you enjoy your meal as quickly as possible. Then Magic Kingdom is a short monorail or walk away.
Enjoy your vacation and Happy Birthday to your nephew.