It's commonplace for literary journals to interview well-known writers and, at some point, to ask them about their process, what their days look like.
When I was a younger woman, back in the days when I longed to call myself a "writer," but knew that I had not yet established any kind of writerly authority to claim the mantle, I remember reading an interview with Graham Greene. He explained how he was able to write one novel per year: he told his interlocutor that he held himself to a standard of 500 words per day-no more, no less-and that, in the course of a year, that would produce a novel.