The Doomsday Clock does not update in real time, but only when the Science and Security Board of the Bulletin of the Atomic Scientists meets. This happens roughly every six months or so, but there is no fixed schedule as near as I can tell. As a result, the possibility occurs where quick crises quickly resolved may go essentially unnoticed.

At the start of the Cuban Missile Crisis, the Doomsday Clock was set to seven minutes to midnight, where it had been since 1960. The Crisis only lasted for a couple of weeks in 1962, between meetings of the Science and Security Board.

In 1963, before the next meeting of the Science and Security Board, the US, USSR and UK all signed the Partial Nuclear Test Ban Treaty, prohibiting all atmospheric nuclear bomb tests. This was viewed as going a long way towards avoiding armageddon, thus moving the clock back to 12 minutes. There is no mention of the Crisis at all in the editorial announcing the change, in fact.

If the Clock updated in real time, it would have undoubtedly have moved much closer to Midnight during the Crisis. As it was, the understandable "stepping back from the edge" that the Crisis was the impetus for did more good for the Clock than the actual event did bad.