As the time is passing, Sphynx is already reading the book, giving it the majority of his concentration. He will still be able to travel and engage in conversation without hindrance or loss of concentration to his reading. Only spell casting or combat should cause him to stop reading.
As it becomes evident, he is quite a voracious reader even without the aid of enhancement like Podren's potion. He is not even sitting still while he reads but walking about while the others discuss and plan, taking in what he hears as well as what he reads.