This isn’t to diminish the importance of a certain (spoiler) Waterbury eight-day clock that's uncovered, but we found it interesting that another Doomsday Clock existed during the time frame of House.
Both John Bellairs and Lewis Barnavelt would have been ten years old in 1948, and the events of the book take place against the global events following World War II and the rise of the Cold War- the development of nuclear weapons, the rise of the Red Scare, and the events leading up to the Korean War.
The nuclear age dawned in the 1940s when scientists learned how to release the energy stored within the atom. Once the Soviet Union developed weapons based around this new energy source there was a heightened concern surrounding the world’s destruction; as a result, the Bulletin of the Atomic Scientists magazine developed a symbol of nuclear danger known as the Doomsday Clock.
First unveiled in 1947, the proximity of the clock’s minute hand to midnight – or catastrophic destruction – has been the magazine’s method of predicting the potential of nuclear war. During its first year the minute hand was 7 minutes away from midnight. The closest to midnight the clock has ever gotten was 2 minutes to midnight (11:58) when, in 1953, the United States and the Soviet Union tested thermonuclear devices within nine months of one another. In 1991 the minute hand was set 17 minutes to midnight (11:43) when the US and USSR signed the Strategic Arms Reduction Treaty, thereby ending the four-decade old Cold War. As of this writing it's 11:55. Do you know where your kids ar - ah, never mind.
The new dimensions of nuclear war terrified the American people, prompting Congress, in 1950, to create the Civil Defense Administration, which brought public fallout shelters, the Emergency Broadcast System, and food stockpiles to the American public. Perhaps the most memorable aspect of the Cold War civil defense efforts were the educational efforts made or promoted by the government. Civil defense classes became standard in public schools where students learned about radiation and basic survival techniques from a nuclear attack. A lot of this education came in the form of public safety films, including the infamous 1951 children's film, Duck and Cover, seen by millions of schoolchildren in the 1950s. And what better place to duck and/or cover than Marshall's post office.
How much of an influence the symbolic Doomsday Clock had on Bellairs is uncertain – perhaps the phrase brought to mind a mundane shelf clock with sinister and supernatural powers that later manifested as the Izard’s clock?
We’re also not sure how thickly rumors about nuclear power were swarming about when John was a boy – he does take a crack at the power of uranium in a chapter of Saint Fidgeta and Other Parodies that’s a parody of teaching materials for a Catholic grade school  – but the concept of doomsday devices popped up in literature and art during the 20th Century when world destruction (or at least the eradication of all human life) was a credible scenario.