meaning - I'll read that book in 2 hours

"I'll read that book in 2 hours."
I'm pretty sure this phrase means that after 2 hours from now I will start reading the book, but I can't stop thinking that it could also means that it will take me 2 hours to read (and finish) that book.
My friend says that for the second meaning the following phrase would be more appropriate:
"I'll read that book for 2 hours." Which also makes senso to me, but I get the idea that maybe I won't be able to finish it in just 2 hours.
Could some native speaker elighten me on this problem? Can the first phrase be interpreted in both ways?
Thank you in advance.