Is this done in EST/EDT? Does it account for developers in India, US, Europe, etc simultaneously or does it convert the time stamps to say, UTC?

The time charts are labeled "local time", so I'd assume they're using ip geolocation or profile info to normalize everyone's times.

You should read the article :)

They used IP geolocation to determine the users local time.

only if it has giant eyeballs and doesn't disappear no matter how hard you try to make it go away... Otherwise, it just seems disingenuous.