Lessee... This is an interesting question that demands some elaboration.
My first draft(of a single chapter) can take anywhere from 2-4 hours to write. Then there's the second draft, which will take another 2-4 hours. Final draft plus final edits takes another 2-4 hours.
(EDIT: Btw, 1 chapter from me is about 4-6 open office pages)
That said, my second and final draft are just me going through the whole draft and editing it thoroughly.