its about efficiency and focus. i go into work and i actually er.. work for that time.
i did the same for uni exams, during exam period i would stay in my flat and revise for about 30 mins and then watch tv or surf the net for 1 hour, then revise for 30 mins. but for those 30 mins i actually focused on what i had to learn. some of my friends went to the library at 9am and came back at 9pm... but as most recent grads would know, exam period in the library tends to be spent chatting with friends. hence they thought they were working for 12 hours straight, and that i was working for about 4 hours a day, but i still got better or similar results.