Not all books are created equal. I'm not the fastest reader, but if I can read a novel in a week or so by just reading 1-2 hours a night. Mathematics texts on the other hand may require as much as 1-2 hours for 1-2 pages (depending on how dense it is). CS texts tend to fall somewhere in the middle for me, but there's a reason that science courses tend to cover half of a book in a semester.