In the book "Revelation its Grand climax At Hand! Published 1988 by the Watchtower Bible and Tract Society." Page 138.
"This convention assembled in Columbus Ohio, July 20-27, 1924. No doubt at the direction of the angel that sounded the third trumpet, a forceful resolution was there adopted and later 50 million copies were distributed as a tract. It was published under the title Ecclesiastics Indicted."
In the book, "Light, Book One, by Judge J.F. Rutherford. Published in 1930 by the Watchtower Bible and Tract Society." Page 135.
"Without previous knowledge or design on the part of any one connected with The Watchtower, the time for the Columbus (Ohio) convention was fixed for July, 1924. Exactly ten years , to the day, from the beginning of the World War the message “Civilization Doomed” was delivered in support of the “Indictment”, which time marked the last typical jubilee; and, showing that the antypical jubilee must begin in 1925, the message announced the doom of Satan’s organization and that the time had come when the people should go free. The year 1925 marked the due time for the great jubilee, and the announcement was made in due course. But the world rulers failed to heed God’s message and to “proclaim liberty throughout all the land”."
It seems they attribute this 1925 to an angel.