Doomsday Clock

As noted by the Twelfth Doctor, the Doomsday Clock was a symbolic clock face representing a countdown to possible global catastrophe, which was started by atomic scientists in 1947. The closer they the clock was set to midnight, the closer the Earth was to disaster. (TV: The Pyramid at the End of the World)

History
When the Monks attempted to gain consent to invade Earth, they reset every clock in the world to resemble the Doomsday Clock. Starting at three minutes to midnight, the clock's countdown predicted how close the Earth was to destruction as seen in a future predicted by the Monks. This version of the clock appeared to be run on automatic, changing to reflect the progression of event and was not directly controlled by the Monks.

As events progressed, the clock got closer and closer to midnight to the point that it displayed mere seconds left when the raoultella planticola bacteria was just a few minutes away from being released into the Earth's atmosphere. However, after the Twelfth Doctor set up an ignition device to blow up the lab and destroy the bacteria, the clock began quickly reversing, signaling the imminent end of the threat. (TV: The Pyramid at the End of the World)