Most of my stories rang from about 12000 words to 20000 words, but I have done closer to 50-60000 on a couple. But I tend to do books that are 12- 20 chapters long.
I prefer Quality over quantity so I don't focus as much on word count as I think other people do. I'm aware that some people may see shorter books as a waste of time, but honestly there are a thousand reasons why a person may not pick up your book. All I can do is tell my best story.
Now in terms of how long it takes me to write a book, I try to write at least 1000 words a day. I edit each chapter as I finish them, and then I edit my complete story as a whole after I'm done. Still, I have to admit sometimes things take time. I can't always power through a chapter, and that's because sometimes ideas need time to develop into something good.
I think I wrote one book in less than a month before, but I wrote another over the course of an entire year simply because it had a lot of complex ideas I needed time to incorporate respectfully.