The astonishing speed of Chinese censorship

You have written something politically sensitive on one of China’s "weibo" microblogging sites. So how much time passes before it gets deleted? And what does it reveal about how Chinese censors work? Computer scientists Jed Crandall and Dan Wallach explain the findings of a study they conducted.
In China, internet penetration has grown massively in the last decade – from 4.6% in 2002 to 42.1% in 2012. Microblogging site Sina Weibo only launched in 2010, but it now has 300 million users and about 100 million messages are sent daily. It clearly plays an important role in the discourse surrounding current events in China.
The Chinese government seems to require Chinese companies to maintain internal censorship regimes.
There have been several interesting studies on how Chinese censorship works and how to work around it, but we wanted to know how the censors do it and how they make their censorship scale to manage hundreds of millions of users.
We found a landscape in which a post could be deleted as quickly as five minutes after being put online and where the censors appear not to work a regular day, but seem to take a break when China’s all-important 19:00 news comes on.
So how did we make such observations?