text: I'd assume you have 4 more months to train, but that should be a good amount of time. Gradually increase you average distance and don't run the same amount everyday obviously. Do a couple of 10 mile days and then on one day run 15. This'll get you used to suddenly running a lot because it'd obviously be torture on your body to run 26 miles everyday. But you could do that once in a while during your training, it'd be a good idea.