Whenever it was written, Revelation aims to encourage Christians during an imperial persecution.
As external evidence they point to the early church writers like Iraneus ( I concluded that John wrote Revelation about A. 96 during Domitian's anti-Christian persecution, which John saw would expand in later years.
I would love to expand this to show both sides, but this came from notes of a term paper.Mc Clintock and Strong, in contending for the later date, declare that “there is no mention in any writer of the first three centuries of any other time or place” (1969, 1064).Upon the basis of external evidence, therefore, there is little contest between the earlier and later dates. When questions of dating biblical books arise, one must consider two main kinds of evidence: external and internal.This has been rendered in English as follows: "We will not, however, incur the risk of pronouncing positively as to the name of Antichrist; for if it were necessary that his name should be distinctly revealed in this present time, it would have been announced by him who beheld the apocalyptic vision.