Just ensure you state your purpose for each book. As long as you're comfortable each book can follow on. One after the other.
After 30 to 40 minutes take at least a 5 minute break. That means getting right away from the work area. After the second 30 to 40 minutes a longer break is recomended, 10 to 20 minutes (not too long less it breaks the momentum too much 
). You know of course not to bother studying any one subject longer than 4 hours even with a break. Research shows that this can actually cause your decline in learning and remembering what you already learnt.
I've experimented with photoreading books one after the other. An hour (with breaks, selecting the next book). I've photoread quite a few books during that hour, some have partially activated for me others I selected for fuller activation.
Alex
