This is probably the most frequently asked question about the book of Revelation. It seems that may people base their interpretation of the book upon the date they believe to be correct. For instance: those who hold the Preterist view must take the 68 date of writing. They believe everything in Revelation was fulfilled with the destruction on Jerusalem in AD 70. Therefore, for their interpretation to be correct, or to even be possible, Revelation must have been written prior to AD 70.
On the other hand, those who take the Historical view believe Revelation was fulfilled during the destruction of Rome in AD 460. They go to a great deal of trouble to prove a later date of writing of somewhere around AD 95. If that date is proven correct, it then in turn disproves the Preterist theory of the fulfillment of Revelation during the destruction of Jerusalem.
So, much of the debate over the date of writing of Revelation comes from the debate over which theory of interpretation is correct. I have read lots of information put out by both sides of question. Both seem to have some good points and some weak points. I have never seen anything that I thought totally proved one date or the other.
Now to the real issue about the date of writing. The only thing we know for certain about the date of writing is that we do not know for sure when it was written. Maybe that is the way it is supposed to be. If the book is interpreted properly, the date of writing makes absolutely no difference. We must understand that Revelation is written in symbolic language which comes from the Old Testament. The events in the OT were "physical," but Revelation is written by taking these "physical" items and events and using them to explain "spiritual" things of the gospel age. For instance: The Tabernacle built by Moses was a literal, "physical" tabernacle which represented something much better to come during the gospel age. It represented the church. See Heb. 8:1-2. Once we interpret the book in this manner, the date of writing becomes unimportant. The message will remain the same regardless of when the book was written.
We know the book was written sometime during the life of the Apostle John. That is really all the is important.