Just like life itself. Let's hurry up with that Doomsday.
The Doomsday Clock is a tradition upheld by an obscure science magazine called the Bulletin Of The Atomic Scientists (a name perfectly suited to its founding in 1945). The placement of its hands is decided by a bunch of scientists and climate researchers, who periodically get together to talk about how worried they are about things in general. So that's the first misconception about the Clock: the only thing it actually measures is the worry of a few people.
In all fairness, said people are esteemed scientists. However, scientists often don't know shit outside their own, narrow fields of expertise, so making a bunch of them from different fields discuss wide-spanning global issues probably isn't all that far from you and your coworkers shooting shit at the water cooler. Sure, you and your office buddies might not run your Fantasy League speculation by several Nobel Laureates like the Doomsday Clock posse does. But since said Nobel Laureates also tend to have very little expertise in the subjects at hand, that's probably for the best.
"So if you follow these calculations it becomes clear that you need to draft a kicker in the first round."
Anyway, the consensus from these meetings is published in the Bulletin, complete with the updating of a symbolic logo they call the Doomsday Clock. That's it. That's the whole thing. What does it mean to be five minutes to midnight instead of six, or ten, or forty? Nothing. And now you know why the Doomsday Clock folks once randomly counted the Fukushima nuclear disaster right up there with Cold War nuclear proliferation, completely ignoring the fact that Fukushima happened because of an earthquake and tsunami while the latter's cause was massively powerful countries locked in a deliberate arms race of mutually assured destruction.