I think it is quite clear that the 1914 date comes from the bible
1914A
Significant Year in Bible Prophecy
DECADES in advance, Bible students proclaimed that there would be significant developments in 1914. What were these, and what evidence points to 1914 as such an important year?
As recorded at Luke 21:24, Jesus said: "Jerusalem will be trampled on by the nations, until the appointed times of the nations ["the times of the Gentiles," King James Version] are fulfilled." Jerusalem had been the capital city of the Jewish nationthe seat of rulership of the line of kings from the house of King David. (Psalm 48:1, 2) However, these kings were unique among national leaders. They sat on "Jehovahs throne" as representatives of God himself. (1 Chronicles 29:23) Jerusalem was thus a symbol of Jehovahs rulership.
How and when, though, did Gods rulership begin to be "trampled on by the nations"? This happened in 607 B.C.E. when Jerusalem was conquered by the Babylonians. "Jehovahs throne" became vacant, and the line of kings who descended from David was interrupted. (2 Kings 25:1-26) Would this trampling go on forever? No, for the prophecy of Ezekiel said regarding Jerusalems last king, Zedekiah: "Remove the turban, and lift off the crown. . . . It will certainly become no ones until he comes who has the legal right, and I must give it to him." (Ezekiel 21:26, 27) The one who has "the legal right" to the Davidic crown is Christ Jesus. (Luke 1:32, 33) So the trampling would end when Jesus became King.
When would that grand event occur? Jesus showed that the Gentiles would rule for a fixed period of time. The account in Daniel chapter 4 holds the key to knowing how long that period would last. It relates a prophetic dream experienced by King Nebuchadnezzar of Babylon. He saw an immense tree that was chopped down. Its stump could not grow because it was banded with iron and copper. An angel declared: "Let seven times pass over it."Daniel 4:10-16.
In the Bible, trees are sometimes used to represent rulership. (Ezekiel 17:22-24; 31:2-5) So the chopping down of the symbolic tree represents how Gods rulership, as expressed through the kings at Jerusalem, would be interrupted. However, the vision served notice that this trampling of Jerusalem would be temporarya period of "seven times." How long a period is that?
Revelation 12:6, 14 indicates that three and a half times equal "a thousand two hundred and sixty days." "Seven times" would therefore last twice as long, or 2,520 days. But the Gentile nations did not stop trampling on Gods rulership a mere 2,520 days after Jerusalems fall. Evidently, then, this prophecy covers a much longer period of time. On the basis of Numbers 14:34 and Ezekiel 4:6, which speak of "a day for a year," the "seven times" would cover 2,520 years.
The 2,520 years began in October 607 B.C.E., when Jerusalem fell to the Babylonians and the Davidic king was taken off his throne. The period ended in October 1914. At that time, "the appointed times of the nations" ended, and Jesus Christ was installed as Gods heavenly King.Psalm 2:1-6; Daniel 7:13, 14.
Just as Jesus predicted, his "presence" as heavenly King has been marked by dramatic world developmentswar, famine, earthquakes, pestilences. (Matthew 24:3-8; Luke 21:11) Such developments bear powerful testimony to the fact that 1914 indeed marked the birth of Gods heavenly Kingdom and the beginning of "the last days" of this present wicked system of things.2 Timothy 3:1-5.