I'd also like to know how long the publishing process process takes once you've finished writing the book. My last question is who reads your unfinished drafts?
Publishing moves slowly--tectonic-plate-speed. Here's how everything breaks down:
You write a book. That can take months or even years. I tend to average 2-3 months for a first draft.
Once you've revised it a few times, you should have other people read it. No one reads my unfinished drafts--for me, it would be like modeling an outfit for someone while only half-dressed... and not in an attractive way. Most of us have close friends or family who read our books first; my husband is always my first reader. Most writers also have beta readers. Betas are other writers or people in publishing who know enough to see the weaknesses in a manuscript and hopefully suggest ways to fix them. Depending on how many readers you have, how quickly they read, and how many revisions you need to make, this can be weeks or months.
Don't query until you're gone through several revisions and really polished your book up. Many first-time authors query too early and when agents request pages, they don't find the writing strong enough to want to read more. This query process also can take months, and that's a whole other post.
Once an agent signs you, he or she will put you through another round of revisions. Don't count on agents and editors to get your book up to professional levels; it should be there before you query. Agents and editors have many, many other manuscripts to choose from and will take on the projects that will sell with less effort on their part; it's a simple cost-benefit analysis.
The agent then submits the manuscript to publishers. This can last months, as well, and I've heard of examples that took years. Use this time to write another book. Or two.
After signing with a publisher, your book is put into the production schedule. If your manuscript was the only project, it could be out in a month or two, but there are a lot of other projects on the schedule, as well. Typical time from signing to release is about 18 months. During this time, cover art and jacket copy will be created. The editor will spend quality time with every word, phrase, and punctuation mark, and he or she may suggest a bunch of revisions.
Once it's ready, it goes into galleys, in which the pages are formatted in book layout and will look like the inside of the book. It will be proofread by several people (both on screen and printed), and then either turned into an "Uncorrected Proof" (some publishers skip this stage) or an ARC (Advance Reading Copy). Printing ARCs and getting them shipped back can take another month or two, and its done with enough lead time to fix any mistakes before they are supposed to go out. We try to get our ARCs into the hands of reviewers at least three months before the release date, and many distributors need information about the book at least six months before it's released.
So, if it takes six months to write and revise a manuscript and another six to query agents and sign with one, a further six months to put the manuscript out on submission to publishers before it sells, then another 18 months before it is released, then the total time would be...
three years, start to finish.
Scarily, that's actually an optimistic guestimate.
Thanks for asking, Tasnim!