What do we know about working times of great living scientists? I am looking for two kinds of data about the great scientists of today, 


Their average daily routine of work. Like how many hours and when? 
Their average length of time of being able to think continuously. 


I vaguely remember seeing a post by Terence Tao about this - like he mentioned that it takes him some x-minutes to focus on a question when he begins working. Though I don't remember if he mentioned any specific length of time for which he can concentrate at a stretch. [..sadly I can't find that post...] 

I am more looking for examples among mathematicians and theoretical physicists though other theory fields might also look more or less the same.
This popular book http://www.amazon.com/Daily-Rituals-How-Artists-Work/dp/0307273601 contains precisely descriptions of working routines of various creative people, including several scientists and mathematicians.