On Feb. 14,1835, during the meeting for calling the first 19th century apostles, Joseph told his audience: "that those who went to Zion with a determination to lay down their lives if necessary, should be ordained to the ministry, and go forth to prune the vineyard for the last time, or the coming of the Lord which was nigh--even fifty six years should wind up the scene." (HC:II, p. 182) This is probably what inspired the three witnesses who picked 11 of the twelve apostles, (Joseph insisted his brother William be picked) to bless several of them that they would live until the second coming of Christ. It also inspired missionaries to warn people that the 'this generation' (theirs, not ours) would be the one to see the "coming of the Lord." This seems very clear, like a typical politician, Joseph later (April 1843) downplays this prophecy with these words from Jesus in D&C 130:14-17: "[Joseph] My son, if thou livest till thou art 85 thou shalt see the face of the son of man, therefore let this suffice and trouble me no more on this matter." Joseph then explains that this statement of the Lord could be interpreted in several different ways, but he
thinks it might mean that Jesus will come by 1890. Of course, the latter words are canonized in the D&C, the former prophecy is not, and nowadays LDS usually emphasize the later, and conceive various explanations for the former.
The Alleged Fifty-Six-Year Second-Coming Prophecy of Joseph Smith:
An Analysis
by
Malin L. Jacobs--Found on the apologetic site SHEILDS.
Thus a prophecy is defended.

God is Love. God is Truth. The greatest problem with organized religion is that the organization becomes god, rather than a means of serving God.