
It’s much better to do it in the moment than to risk losing the contemporaneous inspiration. Don’t be afraid to tear the book up with tags and notations–books are a cheap. Plus you’ll get more for your money this way.
… later, the books were easy to breeze through (see, looking stuff up can be as easy as watching TV) That being said, don’t get bogged down with the names of the cities or the spelling of names, you’re looking to grasp the meta-lesson: the conclusions.
Instead, your energy needs to be spent on figuring out if he’s right and how you can benefit from it. Plus if you already know what happens, you can identify all the foreshadowing and the clues the first read through.