The screenwriter for Star Wars: The Force Awakens and The Empire Strikes Back discusses his process writing the former with J.J. Abrams:
We started walking around recording into an iPhone breaking the story, and we walked for miles through Santa Monica and Manhattan and eventually Paris and London. It was the most fun experience I’ve ever had in terms of breaking a story and shaping it up, walking through some of the most amazing cities in the world and talking to a guy who loves it and is gonna direct it, and you know he’s gonna direct it great. You’re elated by the whole thing. We had a first draft in about six weeks, and then we continued to write it for another two years. We were shooting it and cutting it and there were still little changes being made.
Six weeks to develop Author's Intent. That sounds about right. Any longer and you risk a jumbled mish-mash of competing ideas. The successes I have had in screenwriting or pitching always seem to take shape in six weeks. The hard part is getting people to take a risk on something that developed so quickly.
That is the story of everybody’s life. It happens to be very dramatic for Indiana Jones. Get on the truck, get on the horse. But for you and me, we’re making it up, too. Here’s how I’m going to behave. Here’s what I’m willing to do to make a living; here’s what I’m not willing to do. How we make up our lives as we go. That’s such a powerful idea, because it’s very exciting. It’s the biggest adventure you can have, making up your own life, and it’s true for everybody. It’s infinite possibility. It’s like, I don’t know what I’m going to do in the next five minutes, but I feel I can get through it. It’s an assertion of a life force.