The publication "Your Will Be Done on Earth", 1958, primarily discussed the book of Daniel but also included discussion of other prophetic books. It discussed the period between 1914 and 1926 in some detail and explains why the three and a half times were viewed as three and a half years.
Daniel 7:25 says that the holy people will be delivered into the hands of the "little horn", the seventh world power, "for a time,
two times, and half a time." (Daniel 7 :25)
A time, two times and half a time amount to three times and a half,
or, all together, to half of seven times. The "seven times" that
literally passed over King Nebuchadnezzar during his madness at Babylon
amounted to seven literal years. Measured by this, a half of "seven
times," or three times and half a time, amounts to three years and a
This period of three years six months corresponds with the forty-two months or a thousand two hundred and sixty days during which Jehovah's "two witnesses" were to prophesy dressed in spiritual sackcloth or mourning. (Revelation 11 :1-3) This period began in the first half of November, 1914, and ended on May 7, 1918. On this latter day the president, the secretary-treasurer and the publication writers of the Watch Tower Bible & Tract Society were arrested on false charges.p.181
The calculation of the 1,290 days and the 1,335 days (Daniel 12:11, 12) was counted from the time the desolating abomination was set up.
The setting up of the "desolating abomination" occurred when the worship of the "image of the wild beast," that abominable makeshift for God's kingdom, the League of Nations, was set up by the religious organizations of Christendom . By action of the Federal Council of the Churches of Christ in America this was dated from the close of January, 1919. [...] Consequently this is the point of time from which to count. p.334
Since 1,260 days in prophecy equal three years and six months, then 1,290 days equal three years and seven months . Counted from the close of January, 1919, where do those three years and seven months end?
They bring us to the end of August and the beginning of September of 1922. Unquestionably that Cedar Point convention (September 5-13, 1922) was an impressive marker of the climax of the 1,290 days for the sanctuary class . pp.335.336
And the 1,335 days?
This period would be in addition to the 1,290 days and would be forty-five days or a month and a half longer in prophetic time . It would equal three years eight months and fifteen days. This time period would count from the end of the previous 1,290 days, which had culminated at the second Cedar Point convention in September, 1922 . The following period of 1,335 days would therefore end in the month of May, 1926 . p.337
From 1922 onwards there were spectacular increases, but ...
Evidently, however, there were some who did not `wait' till the end of the announced time, for in 1926 there was a reported decrease in the attendance on March 27 at the Lord's evening meal to 89,278 . [Down from 90,434 in 1925] The year 1925 especially proved to be a year of great trial to many of Jehovah's people . Some stopped waiting and went with the world. p.337
But the grand climax in assemblies [in May 1926] was in London, England, the capital of history's greatest empire, the British Empire . The convention was thus at the seat of the chief backer of the League of Nations, the abominable "image of the wild beast," the political-religious makeshift for the true kingdom of God . From May 24 to 31 the conventioners held their joyous sessions ; and strait-laced, sanctimonious, traditional religious restrictions upon God's people were exposed and discarded, to their great relief . [...] Sunday night, May 30, in London's then greatest auditorium, Royal Albert Hall, came the climax. World powers were then addressed indeed, when President Rutherford spoke to the packed Hall on "Why World Powers Are Tottering-The Remedy" in support of the Resolution that had been submitted to them . In consequence of this putting the seventh world power on notice, the Anglo-American dual world power committed the "transgression of desolation," and the 2,300 prophetic days began to count, to mark off when Jehovah's sanctuary should be restored to its rightful state .-Daniel 8:13, 14, RS . p.338