Every writer is different, of course, but there are a couple of categories into which many, if not most, of us who do it full-time fall: We are distance runners or sprinters, and now and then, both.
Distance runners tend to set a pace and do it over the long haul. Five days a week, six or eight hours a day -- some shorter, some longer -- X-number of pages each day. So if you are doing a 400 pp book and you do five pp a day, then you are looking at four working months for a draft, eighty days. (If you do one page a day, then it's 400 working days, or thirteen-and-third months.
Something usually gets in the way of maintaining such schedules, of course. Life, the universe, and everything. Research, the dentist, the dog has to go to the vet, or you wind up having do do revisions on another project -- the world is full of distractions, so the chapter-a-day is usually theoretical. And if you don't have a deadline, you are less inclined to sit at the keyboard if you have a cold or the flu, so you take the time off. But still, the idea is that you chip away slowly and eventually wind up with a finished book.
Sprinters tend to hit the track at a dead run and go full-out until they fall over. Not uncommon for them to spend fourteen, sixteen hours at the computer. Write for an hour, take a break to go pee, write for another hour, grab a snack, write, and do this for long days and weeks until the book is done. Dean Wesley Smith calls this "burst writing," and used to have a workshop in which the goal was to get a draft of a novel done in a long weekend. It's ass-in-chair until you are done.
My hands won't stand burst writing any more. After a certain number of hours and keystrokes, I'm done. I can't perform the physical action of typing, even with an ergonomic keyboard and frequent breaks.
Now and then, though, it's fun to see how close I can come to my limits without going over them. Which is where the secret project is. I've set a daily page goal that is more that I usually do, if less than I once could. (There were years when I could write 10-15 pp, day in and day out for months. I could party all night long and then work all the next day, too, but alas, not any more ...)
I'll keep you posted ...