I guess folks noted the discrepancy. The WTBTS is attempting to patch up the two endpoints, 1914 & 1918.
The answer to how soon after 1914 is - soon after 1914. Wow.
At this point, it may be helpful to consider what might be viewed as a Bible parallel. Jesus Christ was anointed as the future King of God’s Kingdom in the fall of 29 C.E. Three and a half years later, in the spring of 33 C.E., he was resurrected as a mighty spirit person. Could it, then, be reasoned that since Jesus was enthroned in the fall of 1914, the resurrection of his faithful anointed followers began three and a half years later, in the spring of 1918? That is an interesting possibility. Although this cannot be directly confirmed in the Bible, it is not out of harmony with other scriptures that indicate that the first resurrection got under way soon after Christ’s presence began.
The Watchtower 2007, January 1, page 28 par. 12
- When was Satan cast out of heaven?
Although the Bible book of Revelation does not give the precise time of Satan’s ousting, it does mention a series of events that can help us to estimate when he was cast out of heaven. First among the events is the birth of the Messianic Kingdom. Subsequent to that, “war broke out in heaven,” which led to Satan’s defeat and his finally being cast out of heaven.
The Scriptures clearly mark 1914 as the year when “the appointed times of the nations” ended and the Kingdom was established. (Luke 21:24) How soon after that did the war in heaven break out, resulting in Satan’s ousting?
“The dragon [Satan] kept standing before the woman who was about to give birth,” states Revelation 12:4, “that, when she did give birth, it might devour her child.” This shows that Satan wanted to dispose of the newborn Kingdom quickly, at the moment of its birth if at all possible. Though Jehovah’s intervention prevented Satan from realizing his wicked intention, Satan was determined and relentless in his effort to do harm to the newly established Kingdom. It stands to reason, therefore, that “Michael and his angels” would waste no time in taking action to remove “the dragon and its angels” from the heavenly scene so that no harm could come to the Kingdom. This suggests that the defeat and ousting of Satan took place soon after the Kingdom’s birth in 1914.
Another factor to consider is the resurrection of anointed Christians, which—as Scriptural evidence indicates—began soon after the establishment of the Kingdom. (Rev. 20:6) Since none of Christ’s anointed brothers are spoken of as accompanying Jesus in the battle with the dragon and its angels, the war in heaven and the ousting of Satan and his demons would have been completed by the time the resurrection of Christ’s brothers got under way.
So, then, the Bible does not reveal the exact time when Satan and his demons were expelled from heaven. Nevertheless, it is evident that this event closely followed the enthronement of Jesus Christ in heaven in 1914.
The Watchtower 2009, May 15, page 18