Try [the pomodoro technique][1] if the objective behind your initiative is to reflect-n-improve on your productivity.
> The technique uses a timer to break down periods of work into 25-minute intervals called 'Pomodori' (from the Italian word for 'tomatoes') separated by short breaks. Closely related to concepts such as timeboxing and iterative and incremental development used in software design, the method has been adopted in pair programming contexts. The method is based on the idea that frequent breaks can improve mental agility..

  [1]: http://en.wikipedia.org/wiki/Pomodoro_Technique