How much time should you invest in reading each day to become a buff?
I only spend about an hour each day.
Obviously it depends on how fast you want to become a "buff" and what your definition of a buff is. It seems like your definition is very shallow though judging by your wording.
If you're reading to be an XD book nerd just to know boring facts about books then you're going to burn out pretty quickly. Read at your own pace. Knowledge will come.