If you only have one day, I would reconsider using precious park time at a character breakfast outside the park. You will want to make every minute count, and morning is the best touring time at MK. This park gets busier and busier as it gets later in the day. You can do so much without significant lines the first couple hours after opening. Sit-down meals are nice for breaks, but you don't need one first thing in the morning.
It's also easy to see characters without going to a meal. If a character meal is important, do one later in the day when the park is busy and you are ready for a break -- lunch or dinner at Crystal Palace, dinner at Liberty Tree or dinner at Chef Mickey's.
If you really, really want to do Chef Mickey's breakfast, make your reservation for the earliest time available (probably 8 a.m.), so you can still get to MK around opening time. Another idea -- if the business trip puts you in WDW proximity BEFORE your MK day, do a character meal at a resort one of the other days.