Jacob Neusner said this quote

“ A dear and long-time friend,... asked me, Jack, how long does it usually take you to write a book? I replied, Of course it depends on the project and its requirements, each book has its own rules. But for a statement to the world at large, once I've thought a book through and written it in my mind, it takes me around a week or so, depending on this and that, ordinarily at the rate of a chapter a day, but I've had some two-chapters day and some chapters have taken two days. And then of course there is revision, but around a week is about right. He seemed surprised, and I was surprised by his surprise, so I thought, maybe I'm wrong. I went home and wrote this book, at the perfectly normal pace of a chapter a day, as usual... ”