Yeppers,
12-18 weeks depending on the plan you select. I think Galloway starts you around July4. Now if one were to keep a base up and a long run of 9-13 miles then training can fall backwards just a bit.
Its a great time to shop for plans. Look at what worked (and more importantly what did not) for the recent race. Determine where or if you want to improve performance. Look around for a plan that fits your lifestyle and needs. Regardless of the hype, most any published training plan will get you to the start line if you follow the plan.
For a first timer, look for distance and a gradual build up. Many folks feel an emotional need to run the race distance and the Galloway plan will do just that. Other plans will also get your there but if one has any doubt about jumping from 20 to 26 miles then Jeff's plan is for you.
If you are a little more seasoned, make sure that you only run 3x a week. If that does not sound like enough, understand that I PR'd in all distances as a 51 YO and only ran 3x a week. That does not mean you do not work out 6x a week, but allow the leg muscle and joints time to heal between runs.
Eat a balanced diet. Do not think that I am a runner and move over to a 70% carb diet. Your performance will suffer as will your waist line. Keep to a well balanced 50% CHO diet and you will/may lose a little weight at the same time.
Hope this helps.