Ok maybe I’m wrong that the book Time at hand published in 1889 was his first book but I do believe it was his first in the study in the scripture series. I’ll have to go check the published dates of the other books I have.
I will say this , he may have not believed that all people not of his sect would die at Armageddon but he did write that Armageddon was to take place in 1914. I think both he and Rutherford (for awhile) believed that all their followers would go to heaven and the rest of mankind would be on the earth having issues or suffering or something to that effect.