A Catholic (NB - note a JW apostate) utterly demolishes the JW's chronoprophetic 1914 creed here:
http://catholicnick.blogspot.co.nz/2011/01/1914-house-built-on-sand-jehovahs.html
In doing so he points out as follows a strikingly arbitrary and contradictory application of the 2520 days used to arrive at 1914 and 1260 days used to arrive at 1918:
"Before I conclude, while I was preparing this article, I came across another devastating detail by accident, as I was simply reading over Revelation 11:2-3 ,
1 And a reed like a rod was given me as he said: “Get up and measure the temple [sanctuary] of God and the altar and those worshiping in it. 2 But as for the courtyard that is outside the temple [sanctuary], cast it clear out and do not measure it, because it has been given to the nations, and they will trample the holy city underfoot for forty-two months. 3 And I will cause my two witnesses to prophesy a thousand two hundred and sixty days dressed in sackcloth.” (NWT)
I was stunned when I read this, because verse 2 speaks of a time when the Gentile nations "will trample the holy city," a clear reference to the trampling of Jerusalem Jesus spoke of. Further, the Greek word for "trample" is only used 5 times in the New Testament, and the only time trampling of a city is used is here and (you guessed it) Luke 21:24!! But why are the JWs going to Daniel 4, which doesn't speak of trampling, yet avoid Revelation 11:2 , which clearly speaks of trampling Jerusalem by Gentile Nations? The answer is clear: the time frame Scripture gives for this trampling is 42 months (1,260 days), exactly half of what the JWs claim it needed to be! And after doing some further investigation into this verse, it turns out the JWs ignore any connection with Luke 21:24 (for obvious reasons) and instead claim it is actually a literal 42 months, and this trampling took place between 1914AD and 1918AD when their GB leadership was being jailed for alleged legal offenses. This all too convenient JW response and interpretation is simply ridiculous and clearly done out of desperation."