This post is a question for writers. There is an interesting part of writing a novel that I have long been curious about. I hope some will respond.
You have an idea for a story. Maybe you’ve outlined the story, written a pitch, done some character sketches. Perhaps you’ve worked out some scenes in your head. Maybe for you, a movie plays in your head of the completed chapter and then you can write it down. That’s how it works for me. But at the beginning, it’s an idea, a story known by only you.
Even when the first words go down on the page it still seems ephemeral, more smoke and shadow than substance. Even a couple of chapters into it there’s not much to grab onto; its still like trying to take hold of a cloud. And then, somewhere along the way, it becomes a thing of tangible substance. The fog melts away and there is somehow a foundation where there once was none. There is form and shape. If you look away for a moment and then glance back, it’s still there; it has not dissolved back into the mist. At some point it becomes an entity all its own, independent and somehow able to exist apart from you, its creator. When in the process of writing does that happen for you?
Dark Age Fiction: Jeff Blackmer's Blog 
Mine becomes real after a chapter or two. By then I’ve got the idea for the story, the plot sketched out (my characters might change how I get from point A to point B, but the points stay the same), and the research done. It’s one of my favorite parts about writing – getting lost in a world that seems more real than my own, for a short time.
For me, it’s usually (in a larger story, I never get here with short stories) at the point of putting pen to paper. I start with an idea of who, or what it is I want to write about and then it just takes off. Sometimes I do have to force this process, I’ll admit; most of the time its easy as pie.
For example, with my Work I was invested in the story from moment one. We were writing at our writer’s group and we’d all picked topics to add to the bucket. We were to write about a Scottish man, in New York, wearing a kilt, in the winter. I believe it was a birthday challenge so we were actually writing about one of our members, which probably helped. After about two minutes of writing, I knew that the story was something that wouldn’t just stay at that “short-story-that-never-gets-finished” length. It’s about 40k now, but still has a lot of work to go. The scottish guy, erm, my man, didn’t seem to mind so much that I’d used him as as inspiration either. I do have to say he’s much hotter in real life.
Oh! To answer your question, if I didn’t: Within the first few minutes of writing is when they become real to me.
Too many imaginary friends as a kid? I think it’s possible.
Some very interesting thoughts there, Jeff.
I think it happens during the setup of the story and, suddenly, is in place as the story begins.