Which half marathon? Some have more registrants and thus will have more corrals. If you're in the last one or two corrals, you may not be able to stop for many photos without being in danger of getting swept. And don't forget to allow for bathroom breaks. My advice, if you can, wait until you get to a park bathroom, no lines.
@dreamfinder and
@Texas84, is it safe to assume that most of the Halfs will start in the MK parking lot? That will determine the 1st park the course hits.
The Balloon Ladies are the last to cross the start line. And that's when the 16m/m pace calculation starts. Usually at the mile markers, race staff are available to tell you how far ahead of them you are in minutes. Technically, runDisney could sweep you up to the last tenth of a mile, but I'm thinking once you enter Epcot and are past the International Gateway you should be safe. It would be sad to be swept at mile 12.
Training under Galloway's program for a Half is 19 weeks. You've got plenty of time for any of the 2019 Half Marathons.
Good luck!