The identity of the 7 kings mentioned in Rev. 17:10 sets the timing.
The 7 kings have to be these early Caesers because only those Caesars fit the criteria:
* five of whom have fallen, *one is, the *other has not yet come, and when he does come he must remain only a little while.
NOTE: The count is from Augustus (AD14)because his reign began the Imperial period, his status as the founder of the Roman Principate
Five fallen: Augustus Julius, Tiberius, Gaius, Caligula, Claudius – before Nero
One is: Nero (presently ruling)
One yet to come for little while: Galba – future (reigned 7 months and 7days, shortest reign of all Caesars)
John’s noting the 7 kings with 5 dead, the 6th in power, which is Nero, and one to come makes the timing between 14AD and 69AD…Augustus to Galba… (Nero ruling years 55-68AD…his senate helped him commit suicide in June of 68AD) The fact that John is under persecution as a political prisoner, shows that Nero The Beast had begun his reign of terror on the Christians before that. Galba, succeeding Nero Caesar, would have released John from Patmos in 68 AD*. (John himself mentions he was at Patmos when he received the Revelation), making the Revelation being written before or during 1st half of 68AD while John was still on Patmos.
*Galba was dead by January 15, 69AD………ruled for 7 months and 7 days