Comment by jschulenklopper

Perhaps without realizing that, but essentially you've just described the Pomodoro Technique, http://en.wikipedia.org/wiki/Pomodoro_Technique :-)

It was also my technique for studying for exams through university: 45 minutes of focussed study, followed by a 15 minute break for tea, lunch or fun things. After six of those, I could stop knowing that I had a day well spent. (And as a bonus, I mastered 3-ball juggling after my Algebra-I exam ;-)