How to Improve Concentration with 50-Minute Focus Sessions (workawesome.com)

I think 50 minutes is too long. In any event, this has been well covered in other places:

http://www.pomodorotechnique.com/

http://www.stevepavlina.com/blog/2004/10/timeboxing/

http://www.alljapaneseallthetime.com/blog/category/timeboxin...