scholar, some the WT's publications say that Russell admitted to getting his chronology and some other ideas, including that pertaining to so-called prophetic dates, (at least some of it) from Second Adventists (including from Barbour). Before the Watch Tower magazine came into existence, Russell and Barbour published of a book written by Barbour called Three Worlds, and the Harvest of This World (see https://en.wikipedia.org/wiki/Nelson_H._Barbour ). It mentioned 606 BC, 1874 (or 1873), 1878, 1914, and other daters. I read a much of it online. The above mentioned Wikipedia article says the following.
'Though it bore the names of both Barbour and Russell as publishers, the book was written entirely by Barbour, a former Millerite, who used some of preacher William Miller's teachings as its basis.[2][3] Barbour’s writings were highly influential in the development of Russell’s later teachings, which led to the formation of the Bible Student movement and later, Jehovah’s Witnesses. Its computations of the length of the "times of the Gentiles" mentioned at Luke 21:24, calculated as 2,520 years from 606 BC[4] used an interpretation that is still adhered to by Jehovah's Witnesses.[2]
It used the year-day system of interpreting prophecies, presented the idea of a 360-day "prophetic year" and a historicist interpretation of the book of Revelation.
It drew on the millenarian studies of 19th-century writers in
formulating a system that demonstrated remarkable biblical-mathematical
"correspondencies" and modified Bishop James Ussher's
chronological calculation to declare that 6,000 years of human history
had ended in the autumn of 1873 and that a "morning of joy" was about to
begin for humankind.[2] '
Also in 1877 Barbour published Russell's pamphlet called Object and Manner of Our Lord's Return. That pamphlet book/booklet was Russell's first publication. A PDF of that pamphlet can be read online at https://archive.org/details/TheObjectAndMannerOfOurLordsReturn . See also https://www.jehovahs-witness.com/topic/150248/scanned-pdf-russells-1st-book-object-manner-our-lords-return . The opening post at that web page says the following. "The Object and Manner of Our Lord's Return was C. T. Russell's first
book (or booklet) and has 64 pages. I think this definitively lays to
rest the claim sometimes made that it was first published in 1872 (and
thus before the 1874 prediction) as it's clearly labelled 1877 and in
the text refers to N.H. Barbour, whom Russell did not meet until 1876."
A different post at https://www.jehovahs-witness.com/topic/150248/scanned-pdf-russells-1st-book-object-manner-our-lords-return says the following. "As can be plainly seen in the PDF, Object and Manner gives an
1877 publication date and references Barbour, whom Russell had never
heard of in 1873. Having Russell active in publishing before he met
Barbour makes him appear more independent. However, he got most of his
ideas from Barbour and Object and Manner dates from after he met Barbour."
https://archive.org/details/1875-1880HeraldOfTheMorningAssortedIssues has PDFs of some issues of Herald Of The Morning. A description at that web page says the following.
'1874-1880 Herald of the Morning (assorted issues). Contains scans of
several issues of Herald of the Morning magazine, edited by Nelson H.
Barbour and co-edited by Charles Taze Russell for about two and a half
years. In the summer of 1876, Russell accepted Barbour's understanding
of biblical chronology, believing that Christ had returned invisibly in
1874. Russell and Barbour broke fellowship in 1879 and Russell went on
to start Zion's Watch Tower and Herald of Christ's Presence in 1879.
Russell retained the basics of Barbour's chronology until his death. In
1880, however, Barbour rejected the idea that Christ had returned
invisibly in 1874, opting for a future return of Christ. The magazine
started by Russell is now called The Watchtower and is now circulated by
Jehovah's Witnesses.
The WT at https://www.jw.org/en/library/books/Jehovahs-Witnesses-Proclaimers-of-Gods-Kingdom/You-Are-My-Witnesses-Says-Jehovah/Proclaiming-the-Lords-Return-1870-1914/ has an apparently revised edition of one chapter of their Proclaimers book. It admits the following.
'Russell referred quite openly to
the assistance in Bible study he had received from others. Not only did
he acknowledge his indebtedness to Second Adventist Jonas Wendell but he
also spoke with affection about two other individuals who had aided him
in Bible study. Russell said of these two men: “The study of the Word
of God with these dear brethren led, step by step, into greener
pastures.” One, George W. Stetson, was an earnest student of the Bible
and pastor of the Advent Christian Church in Edinboro, Pennsylvania.
The other, George Storrs, was publisher of the magazine
Bible Examiner, in Brooklyn, New York.
... One morning in January 1876, 23-year-old Russell received a copy of a religious periodical called Herald of the Morning. From
the picture on the cover, he could see that it was identified with
Adventism. The editor, Nelson H. Barbour, of Rochester, New York,
believed that the object of Christ’s return was not to destroy the
families of the earth but to bless them and that his coming would be not
in the flesh but as a spirit. ... Curiously, though, Barbour believed from Biblical time-prophecies that
Christ was already present (invisibly) and that the harvest work of
gathering “the wheat” (true Christians making up the Kingdom class) was
already due.—Matt., chap. 13.
Russell had shied away from Biblical time prophecies. Now, however, he wondered: “Could it be that the time prophecies which I had so long despised, because of their misuse by Adventists, were really meant to indicate when the Lord would be invisibly present to
set up his Kingdom?” With his insatiable thirst for Scriptural truth,
Russell had to learn more. So he arranged to meet with Barbour in
Philadelphia. This meeting confirmed their agreement on a number of
Bible teachings and provided an opportunity for them to exchange views.
“When we first met,” Russell later stated, “he had much to learn from me
on the fulness of restitution based upon the sufficiency of the ransom given for all, as I had much to learn from him concerning time.” Barbour succeeded in convincing Russell that Christ’s invisible presence had begun in 1874. * '