This is a quite unique creation by the labnol.org or very commonly known as Digital Inspiration that let people know the sleeping time and duration of people whom they are concerned about.
Now you must be thinking that how someone could know when and how much time does anyone sleep. And the answer is “Twitter”. This website by the Digital Inspiration www.sleepingtime.org uses the twitter profile of the person whose sleeping schedule you want to know. This website look on the time of all the updates by that person, and on the basis of this, it calculates when the person was least active on twitter and this is how we get the sleeping time of our celebs. Quite unique concept for determining this but should be approximate.