I write first drafts generally, in the span of three months. Sometimes it's less.
The book that is going out to agents this week (finally) was written in a month. Then I spent two years revising it. 9 drafts later, it is finally ready. I've removed characters, removed entire plot lines, cut out at least 30,000 words and added 40,000 more, added more characters, changed both the rising and falling action of the book (kept the climax) and basically tore my hair out and screamed a lot.
I try to write 2,000 words a day. Generally 1,000 words on whatever YA I am working on and then 1,000 on my romance novel/erotica type stuff. Sometimes the word count leans towards one genre more than another. But my other career (I work in a playhouse as a stage manager/director/actor/general go-to girl) gets in the way occasionally. I try to time my books between shows because otherwise I end up conked out on the green room couches with my notebook on my lap.
I try to carve out at least an hour a day to write with no distractions, no internet (unless it is for research) no phone, no IM, no one bothering me (generally). But I'm not married and I don't have kids, so I'm pretty sure that it's easier for me to find the time than for someone who does have stuff like that to deal with. Sometimes I stare at my computer screen for an hour and write maybe 100 words. Sometimes I write 10,000 words without getting up once. Sometimes I just let my cat sit on my computer and see what words his butt pressing into my keys comes up with
I also have great critique partners who do a fast draft 1,000 words a day minimum challenge every few months. It helps to have other people egging you on in this craziness
