These countdown things can get a bit tricky when they are world-wide. This comes about due to the rotation of the Earth and the placement of the International Time Line. Because of this it is most likely that, should the Rapture actually happen on the 21st of May, then Australian Christians will be raptured about 14 hours before our American friends—assuming God complies with International Time Line convention.
I also need to make it very clear that the Rapture is NOT the same as the end of the world. On Rapture day bona-fide Christians will be removed from the Earth and relocated by God to a much better place, which may or may not be Heaven. There seems to be some uncertainty about where they get Raptured to. But the key point here is that the world does NOT end on rapture day. Should the Rapture take place then those not raptured can reasonably expect the world to end about five months later, most likely some time in October. Basically, according to the Rapture experts, the Earth will go up in flames about five months after the Rapture. The very soil will ignite and burn.
I just wanted to clear this up because I have seen a lot of reports in the papers and on the TV where they are saying that the world will end on the 21st of May and this is simply incorrect. That is not going to happen. The Rapture happens slightly before the end of the world. You would expect them to research these things a little better. Really.