Try forgetting Valentine's Day or your anniversary and see what happens. You will not likely forget them next year. See, dates are often a key element in our lives. They can denote a beginning or an end.
Dates can also affect other events in our lives.
So it was with John's writing of the book of Revelation. There are two dates that are generally considered, A.D. 96 and A.D. 66 - 68. Currently, the A.D. 96 date is far more popular. However, many who hold this date admit that although they believe this date is probable, it is not definite. The main basis for their conclusion of the late date is generally given as being supported by a statement reported by Eusebius in about A.D. 325.