Today's "Rapture-at-any-moment" folks rely on the ambiguity. They've been saying the end is near since the 1840's when the the Dispensationalist doctrine was first invented. They used to be more forthcoming about predicting actual dates, but they've got more cautious about that since they've been burned so many times. Nowadays, they'll just say, "it's near!"
The wacko environmentalists have never been shy about picking specific dates for stuff—here is a collection of some of them:
https://cei.org/blog/wrong-again-50-years-of-failed-eco-pocalyptic-predictions/
They count on the mass media not calling them out on their lunacy.