Setting dates is not unique to Millerism. If you read (and you should) Froom's massive history of millennialist thought, Prophetic Faith of Our Fathers, you will find that the practice has an ages long history. Age to Come Believers (Literalists) were as prone to do that as Millerites, and in fact did it before Miller. One example is Aaron Kine, a Congregationalist clergyman, who focused on a date in the 1830s. Another is the German Lutheran expositor Bengel who predicted Christ's return for 1836. Both preceded Miller and did not hold Adventist doctrines. Speculation about dates appears in almost every era.
Millerite evangelists read Literalist works. Any transfer of thought was from Literalists to Adventists, not in the other direction. Millerite Adventists tried to suck Literalists into Adventism.
Joshua V. Himes recalled the attempt in terms that show the exchange as less than pleasant:
The Millennarians [sic] holding these views and looking for the speedy coming of Christ have become very numerous in England, Ireland, and Scotland. Indeed some of the brightest lights of those countries are of that school. In 1840 an attempt was made to open an interchange between the Literalists of England and the Adventists in the United States. But it was soon discovered that they had as little fellowship for our Anti-Judaizing notions as we had for their Judaism, and the interchange was broken off.
Himes defined the difference between Literalist and Adventist belief this way:
The distinction between Adventists and Millennarians, is, – The Millennarians believe in the pre-millennial advent of Christ, and his personal reign for a thousand years before the consummation or end of the present world, and creation of the new heavens and earth, and the descent of the New Jerusalem. While the Adventists believe the end of the world or age, the destruction of the wicked, the dissolution of the earth, the renovation of nature, the descent of New Jerusalem, will be beginning of the thousand years. The Millennarians believe in the return of the Jews, as such, either before, at, or after the advent of Christ, to Palestine, to possess that land a thousand years, while the Adventists believe that all the return of the Jews to that country, will be the return of all the pious Jews who have ever lived, to the inheritance of the new earth, in their resurrection state. When Abraham, Isaac, and Jacob, with all their natural seed who have been of the faith of Abraham, together with all pious Gentiles, will stand up together, to enjoy an eternal inheritance, instead of possessing Canaan for a thousand years.
The Millennarians believe a part of the heathen world will be left on the earth, to multiply and increase, during the one thousand years, and to be converted and governed by the glorified saints during that period; while the Adventist believe that when the Son of Man shall come in his glory, then he shall be seated on the throne of his glory, and before him shall be gathered all nations, and he shall separate them one from the other, as a shepherd divideth his sheep from the goats. He shall set the sheep on his right hand, and the goats on his left. That one part will go away into everlasting (eternal) punishment, but the righteous into life eternal. They cannot see any probation for any nation, either Jew or Gentile, after the Son of Man comes in his glory, and takes out his own saints from among all nations. They also believe “God will render indignation and wrath, tribulation and anguish upon every soul of man that doeth evil, to the Jew first and also to the Gentile, in the day when God shall judge the secrets of men.”
The Millennarians believe that the saints must have mortal men in a state of probation, for a thousand years, as their subject, in order for them to reign as kings; for, say they, how can they reign without subjects? To which the Adventists reply, If it is necessary for them to have such subjects for a thousand years to reign, by the same rule they must have them eternally; for “they shall reign forever and ever.” – Rev. xxii:5.
As you should see, Millennairians (Another term for Literalists) held views Russell shared. Russell did not hold Adventist views. This is from Schulz:
Russell did not read anything Miller wrote. “We have been unable to secure Mr. Miller's writings to compare his Interpretations,” Russell wrote. “We have merely learned the dates at which he applied the prophetic numbers.”[1]He accepted no doctrine unique to Millerism. “We are not endorsing the teachings of Brother Miller,” he wrote. Russell saw Millerism as the starting point of an intense scriptural examination, but the doctrines he pointed to as the favorable result were not at all those of Miller.[2]
Russell made this his connection to Millerism clear in The Time is at Hand. He saw Millerism as a preliminary separating work, part of the fulfillment of the parable of the Foolish and Wise Virgins which he saw as prophetic rather than merely illustrative. Despite any “prophetic” role Millerism may have held Russell rejected the theology:
While, as the reader will have observed, we disagree with Mr. Miller's interpretations and deductions, on almost every point, – viewing the object, as well as the manner and the time, of our Lord's coming, in a very different light, – yet we recognize that movement as being in God's order, and as doing a very important work in the separating, purifying, refining, and thus making ready, of a waiting people prepared for the Lord. And not only did it do a purifying and testing work in its own day, but, by casting reproach upon the study of prophecy and upon the doctrine of the Lord's second advent, it has ever since served to test and prove the consecrated, regardless of any association with Mr. Miller's views and expectations. The very mention of the subject of prophecy, the Lord's coming and the MillennialKingdom, now excites the contempt of the worldly-wise, especially in the nominal church. This was undoubtedly of the Lord's providence, and for a purpose very similar to the sending of the infant Jesus for a time to Nazareth, “that he might be called a Nazarene,” though really born in the honorable city of Bethlehem.
[1] C. T. Russell: Thy Kingdom Come, 1898 edition, page 87.
[2] C. T. Russell: Making Ready for the Reign of Righteousness, The Watch Tower¸ November 1, 1914, page 325.