Just make sure you understand everything properly and that you really do return to it multiple times later to make sure you're not just going to forget it again. 

Otherwise it would be a bit like blitz play: seeing ideas without really understanding them, mostly just in one ear and out the other.

I used to spend way too much time trying to remember every intricate detail of every chess book I read. I've since realized that even if I don't remember and absorb every detail, just being exposed to lots of positions will leave a vague memory in my mind that might come in handy later. Reading redundant books and/or re-reading the same one will cause me to finally remember things after being exposed to them several times.

Thus, I've realized that I'm better off going through lots of material quickly, then going through the same stuff again later if I really feel I need to remember all the details. That doesn't mean that I'm just flying through the material with no comprehension, though. If I have a question while reading it the first time, I'll stop and make sure I understand. But I really don't feel the need to try and get every detail perfect the first time. Repetition is key to remembering, but you need to put some time between repetitions, rather than just spending an hour repeating the same stuff over and over.