Apocalypses are lots of fun. They bring excitement to our otherwise boring lives. They smash through the smug façade of everyday authority. And it’s a blast to imagine the exact manner in which divine punishment will rain down on this wicked world—the way the buildings will crumble and the cars will crash and the luxury vacation spots will be incinerated by lava—while we, the virtuous, are spared.

One thing that any start-up prophet should have learned by now, however, is to be a little hazy about dates. Sure, a big part of the end-times entertainment is deciphering a precise…