barry
You ask about the three and half years from 1914 to1918 should better be understood as 1260 years instead. There are numerous theories as to how this specific time element should be applied and I would suggest that you stydy carefully what WT publications have stated on this matter. What is most essential for understanding such time elements is the context and the context as shown by Daniel and Revelation is that this event would be applied to the last days or the time of the end soon after the birth of the Messianic Kingdom in 1914 and would concern itself with developments of the true religion or church in that period.
scholar JW