sometimes overnight, sometimes years!
i usually read before sleeping so i tend to, well, fall asleep. and i forget where i've left off, so i have to read some pages back over and over again. and sometimes i misplace the books and find htem years later. like in the case of anne frank, which i started reading in high school when it was given to me as a gift and which i've finished reading in college, when i found it in one of my forgotten boxes.