Russell was indeed a speculative theorist who grabbed mostly other people's ideologies and concepts, Pyramidology being one.
Christ's return was seen by himself and others at the time something to preach and sell through literature publishing.
I still find it surprising that those men actually thought the great pyramid of Giza was the stated monument god left for mankind, in light of the real ancient Egyptian religious use and practice ?
Nevertheless selling Jesus's return and the great day of Armageddon was sold and preached all throughout the 20th century by the WTS and it still does by the WTS/JWS organization to this day.
The truth to this date setting by the WTS (1874, 1914, 1975 etc.) was that it was an act of unscriptural apostasy against Jesus's own instructions for preaching his new Kingdom order.