Depends on what you consider an novel and if I've already read it before. When I was re-reading the Twilight Series I read the last book in about 4 hours. I remember it creeped my teachers out in middle school when for in class reading day I took the entire chronicles of Narnia and got through almost all of them in one day (that was in elementary school)

Right now I'm reading Margret Atwood. Her stuff is a bit harder for me to read because it has so many nuances so it's probably going to take a week or two for me to get through.