The outdoor characters at MK tend to have shorter waits, especially if you time it right for their first set, or when they're coming back from break. I've met Peter Pan and Wendy, The Tremaines, Fairy Godmother, Snow White, and Mary Poppins all with <5 minute waits (maybe 1-5 families in front of us). They do move the characters around some, and it can depend on where they're standing and how visible they are. We've walked up to Mary Poppins standing alone under the awning by the Main St confectionary, but when she's out in the street a bit further she may have a wait.
Gaston is the longest I've waited for a character outside, we were waiting about 10 minutes before he was scheduled to come out, with 5 groups already in front of us last October. I think he came out a couple minutes late as well, and by that time there were at least 5 more groups behind us.