There are two extremes: Bright Shadow took fourteen years to write from the time I began it until I had the published book in hand. S.O.R Losers was written in two days. The reason for both provides an answer to the question.
When I was in high school, I was on the soccer team, a team created by the school for boys who were not particularly athletic. There were twelve of us, only one of whom had ever played soccer before. I was not even on the starting team of eleven.
On the day of our first game, our goalie quit the team. Our coach, when he belatedly heard the news—just as we were heading for the field–looked around, pointed to me and said, “Avi, you’re the tallest. You’re playing goalie.”
Needless to say, we lost that game, and went on to lose every game (two seasons) we ever played.
Years later, my boys (who were soccer players) loved to hear how bad a player I was, and how bad my team was. That’s to say I rehearsed the story (with embellishments) a fair number of times. When I decided to write the story, it was all in my head, and life. It was exceedingly easy to write.
By way of contrast, Bright Shadow entered my thoughts, not as a story, but as a riddle.
When bright, it’s dark, when darkest, it’s gone. When gone for good, so are you. What am I?
I don’t know where this came from, or why, though I do like riddles. Perhaps I had recently learned that Anglo-Saxon culture considered riddles a form of literature.
The point is, I liked the riddle. I then went on to try to create a story that fit it. That’s to say that the plot of the book was in itself a kind of riddle. It took a very long time to figure it out.
The point is that the two books were created by diametrically different methods: S.O.R. Losers came out of personal experience. Bright Shadow was an intellectual exercise.
My own sense is that creating books are best written by a mixture of both—experience and intellect—which in my case means it takes me about a year to write most of my novels. Sometimes a little more. Sometimes a little less. But to answer the question, How long does it take you to write one of your books?—a year is average.