Hi Blair!
RunDisney vacations are the best! My family loves taking them and there are races for all of us at each weekend!
The race dates for 2015 have not been set yet. If you look at the 2014 dates, they will be very similar as most races stay on the same weekend every year. (but keep in mind that races are always subject to be added or deleted from the calendar)
In 2014, these are the race dates:
Walt Disney World (Florida)
Jan. 8-12 Walt Disney World Marathon weekend
Feb. 20-23 Princess Half Marathon weekend
May 2-3 Expedition Everest Challenge weekend
Oct. 3-4 Twilight Zone Tower of Terror 10-Miler weekend
Nov.(TBD) Wine and Dine Half marathon weekend (it's generally the 2nd weekend)
Disneyland (California)
Jan. 16-19 Tinkerbell Half Marathon weekend
Aug. 28-31 Disneyland Half Marathon weekend
I hope this helps give you an estimated time frame. You can keep watching on the
runDisney website for future dates.