Russell in his The Time is at the Hand writes:
As shown in the accompanying diagram, the period of their favor, from the commencement of their national existence at the death of Jacob, down to the end of that favor at the death of Christ, A.D. 33, was eighteen hundred and forty-five (1845) years; and there their "double" (mishneh)--the repetition or duplication of the same length of time, eighteen hundred and forty-five (1845) years, without favor--began. Eighteen hundred and forty-five years since A.D. 33 shows A.D. 1878 to be the end of their period of disfavor. A.D. 33 plus 1845 = A.D. 1878.
He came to 1845 years as twice the age of dispersions:
"And first [before the favor will come] I will recompense their iniquity and their sin double." The Hebrew word here rendered "double" is mishneh, and signifies a second portion, a repetition. Thus understood, the Prophet's declaration is, that from the time of their being cast off from all favor until the time of their return to favor would be a repetition, or duplication in time, of their previous history, during which time they had enjoyed divine favor.
Israel's dispersion among all nations since the close of their 1845 years of favor, and no other of their captivities, fits this pointed expression--a land which ye and your fathers have not known. So then this, together with the no favor, positively marks this prophecy as relating to Israel's present dispersion among all nations.
ISRAEL AFTER THE FLESH:
From the Death of Jacob to the Cross, the Period of Favor to the Nominal House of Servants, 1845 Years, Followed by the Exaltation of a Faithful Few,
and by Casting off, Trouble and Judgments upon the Others
ISRAEL AFTER THE SPIRIT:
From the Death of Jesus to A.D. 1878, the Period of Favor to the Nominal House of Sons, 1845 Years Followed by the Exaltation of a Faithful Few,
and by Casting off, Trouble and Judgments upon the Others
Russell believed that the dispersions started:
with Length of Favor 1845 Years, from Jacob's Death to Israel's Rejection and the Beginning of Spiritual Israel, A.D. 33
Length of Favor, 1845 Years, from Jesus' Death to the Beginning of Christ's Reign and the Rejection of Babylon, A.D. 1878