The Nuclear Doomsday Clock is a symbolic representation of how close the world is to catastrophic destruction by nuclear war. It is based on the real-world Doomsday Clock, which performs a similar function. The closer the clock stands to midnight, the nearer the world is to Armageddon.
The cover page of each chapter of Watchmen has an image of a clockface. The clock on the cover of Chapter I is set at twelve minutes to midnight, and on the cover of each subsequent chapter the clock is moved forward by one minute. The clock on the cover of the final chapter, Chapter XII, is set to midnight. The final page in each Chapter also bears a clockface showing the same time as the one on the cover.
Veidt's master plan takes place at midnight, New York local time. On page 27 of Chapter XI, a clock set to New York time is pictured at one minute to midnight. A clock, covered in blood and set to midnight, appears on the cover and first page of Chapter XII.
During the opening and conclusion of DC Universe Rebirth, a watch formerly owned by Wally West is shown. One of the gears is shown to be rusted and worn down, preventing the watch from functioning. Doctor Manhattan, son of a watchmaker, repairs it. Upon doing so, the watch begins to tick backwards, before taking on the appearance of the Doomsday Clock. Unlike in Watchmen, this symbolizes Doctor Manhattan's rewinding of history, rather then the countdown to armageddon. Moreover, it represents his intention to do so again.
- Doomsday Clock at Wikipedia, the Free Encyclopedia