I think what you're describing is something similar to pomodoro technique (http://pomodorotechnique.com/), only on bigger scale (8 hours at once). Maybe you will find it useful.
I tried pomodoro but never sat well with me. I can focus for 1-2 hours happily once I'm into something. I worked in a team where it was pushed as a mantra for working. The issue with that being is that everyone was on a different schedule. I actually considered it a way to attempt to kill social interaction within the team, say going for coffee together.
If it works for you, go for it, but I do not work in 25 minute chunks.
