Post-Apocalyptic modern world, a group of civilian survivors about three dozen in number find themselves trapped in a military base. They have no way out except by air.
The military base has a dozen helicopters but none of them knows how to fly the damn contraption. Assume they have endless food, fuel, and time, and access to training and operating manuals, video, etc, for the helicopters.
What is a reasonable time frame for at least one of them to learn how to pilot that on their own, assuming they are of average intelligence and ability?
EDIT: I'm not looking at exceptional cases, stroke of luck, or Hollywoodian handwavium. I asked for a reasonable, realistic timeframe.