Threats
The first week inside [The Pure Trees] tested Khan's physical and mental limits. Attending lessons that heavily focused on his mind for twelve hours a day, fusing them with his regular training, and leaving some time for Liiza forced him to sacrifice his sleep often. He even had to forsake his naps on Snow's back to fit his mental exercises and meditations at times.
The problem wasn't with Khan's ability to manage his time. He simply had too much to do, or, rather, he didn't want to forsake any aspect of his life.
His companions didn't have it as bad as Khan. Only George and Veronica attended Professor Supyan's additional lessons, but the girl decided to stop going after only two days. Instead, the other recruits didn't even bother to try them, no matter how much George praised them.