To those who ascribe to Christian teachings found in the Bible, Jesus Christ said in Mathew 24:36, ""No one knows about that day or hour, not even the angels in heaven, nor the Son, but only the Father.' (New International Version (©1984)). It doesn't say we won't know the general time, though, at the close of this present age, often referred to by believers as the '"end time" or "last days" of this age.
In Matthew 24:22, Jesus said, "If those days had not been cut short, no one would survive, but for the sake of the elect those days will be shortened."(New International Version (©1984)).
Now, if one doesn't hold to these teachings, then they may not believe in any doomsday scenario. Alternatively, they may believe in a doomsday or apocalypse and their views and beliefs may have absolutely nothing in common with the beliefs of Christians or other religions that hold to the above teachings in the Bible.
Entitled to their own beliefs, they may set a particular date as this poster has done and strongly believe in it. Therefore, rigorous study is the course of action to take to probe whether a belief is true and accurate - or not. It's up to each of us individually to do this for ourselves. We shouldn't take the word of any man or woman, but prove all things through research, study, and through prayer if one in fact does believe even in prayer.