This has worked for me several times...
There are undoubtedly better programs, but for me and my busy family and professional schedule, this approach, requiring running only four days per week has secured some reasonable times for an aging guy:
-One day a week, run your "distance." (Whatever you can do with relative comfort, to start. I usually begin at six miles, then go up two miles every two weeks. This way, in month one, I do a six-mile distance the first two weeks, then an eight-mile distance the second two weeks. The second month, it's 10's and 12's; the third, 14's and 16's, then 18, 20, and 22 the final (or fourth) month. This can be stretched out as far and over as many months as you want, but remember that the "next distance" is almost always hard the first time out--don't expect to run six miles each Sunday for a month and then have a great time running eight miles the next: Be safe, but push through it.)
-One day a week, run a "half-distance." Typically, I try to put this in the middle of the week, as far as possible from my distance.
-One day a week, preferably on a treadmill, run hill intervals, keeping your speed at roughly marathon pace (whatever you hope for or is realistic) and alternating each minute from (more-or-less) flat to increasing inclines, for 30 minutes. If you exhaust yourself, go "flat" for a few minutes, catch your breath, and start over.
-One day a week, on a treadmill or outside, run speed intervals, similar to the hills, but changing the pace instead of the incline.
-Other days are options. I usually rest or run very lightly, if I have time.
**Be careful on a treadmill. Use the safety strap, especially until you know what you're capable of.
**On race day, especially at WDW, you'll be inspired and hyped. DO NOT GO OUT TOO FAST: Run your trained pace, and pick it up at the end if you still have the steam. Drink water and Gatorade in alternating, small amounts, and get some carbs in yourself EARLY, before you think you need them. Once you've bonked, it's way too late.
Good luck.