|My first release, now in audio:Macbeth's Niece|
That's a little like "How many angels can dance on the head of a pin?" It's part practical, part philosophical, and mostly unanswerable.
We all know authors who take years to write a book. Some of them are quite self-righteous about it, copping a "you can't rush genius" attitude. I'm no genius, so I can't say if that's true. I've noticed, however, that the rest of us are writing as fast as we can, and while it used to take two years minimum to get a new book out, most publishers are fine these days with more than one a year.
That can lead to some loss of quality, and readers with an editor's eye bemoan the modern tendency to rush to get a book out. Still those same readers go on Facebook or Goodreads and wonder when Author X is going to stop dilly-dallying.
My writing process begins with a rough draft that's pretty terrible. When it's finished, I put it out of sight for a few weeks then go back and rewrite to make it less terrible. There's also what authors call the muddle in the middle, a point in writing a book where you've made such a mess of things that you don't think you can write your way out. Sometimes all you can do is give the muddle time to resolve.
Then there's editing. It takes time to read a book and thoughtfully decide what has to be changed, what might be changed to make it better, and what doesn't need changing but should be tweaked. Good editors take that time, so it generally takes a few back-and-forth exchanges between editor and writer to get to a point where they agree the book is solid.
To answer the question, then, these days I shoot for six months. A rough scenario might be four weeks for the rough draft, two weeks "rest," two weeks to revamp. My first reader takes over then, and in 2-4 weeks I'm making changes she suggests. Then the editor goes at it, and we back-and-forth for a month or two. When that's done, I submit to the copy editor, who irons out the leftover wrinkles.
That's if all goes well, of course. There are times when one or more of those things takes longer, which sets the whole process back. And of course life intervenes sometimes and says, "You won't be writing this week, so just accept it."
I didn't mention research yet, but I spend a lot of time finding out things I don't know and checking on things I might or might not know.
A caveat for those just starting out: this is my process after twenty-plus books. It took me MUCH longer in the beginning. The "one book a year" advice is probably a good starter's rule, because as a newbie, you really don't know what you don't know yet.