How many hours a day did Stephen Hawking study?

Could you please elaborate on the daily study habits of Stephen Hawking? Specifically, I'm curious to know how many hours a day he dedicated to his academic pursuits. Was he known for his rigorous study schedule, or did he have a more flexible approach to learning? Additionally, did his physical condition play a role in shaping his study routines in any way? I'm fascinated by the balance he must have struck between his intellectual pursuits and the challenges he faced throughout his life.