I am a somewhat fast reader. It isn't like I can finish those huge Harry Potter books in two hours or anything, but generally if I pick up a YA novel and have free time, I will finish the book that same day. Last night I started AN ABUNDANCE OF KATHERINES and read for about an hour and a half. This morning I lounged around and finished it. I wasn't keeping track, but I think I put in three hours total.
That's almost sickening when I think of how long John Green must have toiled away on the thing. I haven't seen his stats anywhere. I guess it could have been anywhere from three months to over a year. Still, that is A LOT of hours of work compared with how much time readers will spend with it.
When I finished my first manuscript, I sent it out to several readers. One (who is notoriously fast) was done in two hours. TWO HOURS! Considering how much time it takes me to write and revise, that is probably the equivalent of the time I spent on each page!
That's the way it is. There's nothing wrong with it, but sometimes it's mind-blowing when you really stop to think about it.
At the same time, a writer might spend a year of their life on a writing project. A reader might only spent a few hours with it, but it might change their life forever.