doomsday clock 

The clock that shows how close humanity is to "Midnight", a nuclear holocaust. As of 2002, the clock sits at 7 minutes to midnight.

In 1984, the doomsday clock was at 3 minutes to midnight.

doomsday clock by Gann June 3, 2006

Doomsday Clock 

A timepiece that counts down to the exact time of a deadline, failing to complete a certain task by the end of that deadline will result in dire consequences.

May refer to a metaphorical doomsday clock i.e. watching an actual clock and doing the math to see how much time you have left.

Or a physical doomsday clock like the ones that were sold in the lead up to the millennium or the ones featured on bombs that explode once they reach zero.

John started keeping time on the doomsday clock after his boss had told him he'd be fired if he hadn't finished all of his paperwork before 6pm on Friday.

Or

For dramatic purposes whenever you see a bomb with a doomsday clock on TV or in the movies it always stops with just one second to spare.

Doomsday Clock by The Captive Spirit September 7, 2010

Doomsday Clock 

A bunch of eggheads got together and decided this whole humanity thing wasn't really working out, and that there should be a definitive scale available for people to plan ahead for their weekend. Measured in "minutes to midnight", it aims to provide a realistic expectation of the likelihood of having to go that social engagement you've been dreading, with any mention of "seconds to midnight" providing a valid excuse for having one more drink, since your chances of living to experience the hangover are drastically reduced.

According to the Doomsday Clock, it is now 30 seconds to Midnight

Moscow Mule, anyone?

Doomsday Clock by Kolltomnus November 5, 2023