I read it over two days while studying for an exam in class (devoted about half of each day to reading it so equivalent to a full day). I read lippincotts about 2 months ago and annotated my FA with it so I only read RR Biochem to refresh my memory and fill in any gaps. It's a good book and if I could do it over again I wouldn't have even touched lippincotts. If you're reviewing biochem for the first time, it might take two or three days to really absorb it. Also, the FA Biochem section is horrible and you're going to have to annotate it like crazy to make it more understandable.
Also, this question is for anyone who has a better understanding of how biochem is tested on boards. I reviewed biochem and made a real good effort to understand all the pathways, how everything is interrelated and regulated. After doing a lot of questions in biochem it almost seems like they don't care about that. Most questions are just about some stupid enzyme defect where you just regurgitate info from some list of diseases you memorized, a single pathway that goes wrong, or a missing vitamin. Is this how simple the biochem questions are on the boards?