Every time I do a school visit, I inevitably get asked, "How long does it take you to write a book?" It's a fair question, but the answer is, "How long is a piece of string?" It's different for every book, and it can also depend on whether someone is waiting for it (i.e. a commissioned work). People often say, "Gee, you're so prolific", which can feel like a criticism, but I loved to hear about Monet and how he would paint all day and complete 8 or 9 works in that time.
It's all practice. Some practice takes longer. Some things take longer to learn. Some books take longer to "get right". Plus, I write chapter books as well as novels, so a chapter book might only be 2000 words. Ray Bradbury used to write a short story a week - some of his writing advice includes 'Don’t start out writing novels. They take too long.
Begin your writing life instead by cranking out “a hell of a lot of
short stories,” as many as one per week. Take a year to do it; it simply isn’t possible to write 52 bad short stories in a row.'
It's the same with picture books and chapter books. Write a picture book or a chapter book every week for a year and you're sure to come up with a few gems! In order to do that, you'll need a list of ideas. Bradbury is also famous for writing a huge list of words and then writing a story about each one. (Read Zen in the Art of Writing where he describes this.)
What about novels? John Creasey, who wrote 564 books, said, 'How many words a day do I write? Between six and seven thousand. And
how many hours does that take? Three on a good day, as high as thirteen
on a bad one.' Wow. Georges Simenon wrote 75 novels and
28 short stories about his detective character, Maigret. Simenon also wrote around 300 other novels and
novellas, plus pulp fiction (under more than two dozen pseudonyms) and
nonfiction. He was apparently able to write a novel in just a few days, but The Guardian has a quote from him that made me wonder what drove him: "Writing is not a profession but a vocation of unhappiness." Hmmm.
Right now, I'm back writing my two pages (or 30 minutes) minimum per day. It works. On bad days, I make sure I do the minimum; on good days I write more. Earlier this year, because I was writing a novel for my fourth semester at Hamline's MFAC program, this routine led to me finishing a 66,000 word YA novel. I didn't plot this one out beforehand so it was like writing in the dark - nervewracking. There were many days when I sat with no idea what would come next. But the 30 minutes minimum kept me at it.
Revision is different. I can spend two hours on the same pages it took me 30 minutes to write! But I also think other aspects tie into whether you are prolific or painstaking. (Painstaking to me is four years on one book.) One is simply typing speed. In high school I took typing as a subject instead of biology. I still have no desire to cut up frogs, but I type fast. Another is to do with plotting. I think if you know where you are going you will write faster and write more (feel free to disagree).
Another is to do with style and language. I suspect that literary writers take a lot longer to write - they are painstaking about language and sentences. Or maybe they need more thinking time? I love to be swept along by my characters and the story, but then my second and third and further drafts have to slow down and focus more on filling in the details.
So whether you're prolific or painstaking, the only thing that will get you to The End is perseverance. The pleasure in being prolific is that you get there faster!