The characters are normally out between 9:00AM to 11:00AM, and are located at either the Gangway, Rustmore, Post Office, Marge's Barges, Scuttles Cove. There's also a dance party at the Gazebo at 12:15PM.
I've done the 5K before and were able to see the characters at all the places except the Gangway since that's back at the boat.
You can look up past navigators for times and locations.
Cheers!