You know how, now and again, a group of people calling themselves Christians comes out to embarrass the faith and make all the sane Christians look bad? Yeah. It's that. At least it's not as bad as Westboro.
Essentially, they claim that despite the words of Jesus saying that we cannot know the day of his coming, we can. Their reasoning basically comes down to the fact that the Bible has some 5s and 21s in it, as well as some other deep study of the Bible that their website never even begins to divulge. Also not sure how they get the end of the world coming only a few months after the rapture; even in a pre-tribulation interpretation of Revelation I've never heard the process between rapture and finale as being that short.
So in other words, it's one of two things; 1) idiots coming up with ridiculous biblical theories by taking statements out of context and ignoring blatantly conflicting passages, or 2) people trying to use religion to make money. Either way, it will once again make Christians look bad even though the vast majority of them are not near this ridiculous. Sigh...