The late Martin Hengel in his Johannine Question (p. 81) wrote:
His ‘school’ or sphere of activity is to be placed firmly in the context of the Christian communities of Asia Minor in the last decades of the first century. The Apocalypse could be an earlier work, the nucleus of which was written in the time after the shock of the Neronian persecution, the beginning of the Judean war, the murder of Nero and the civil war; possibly it was reworked later, early in the reign of Trajan, by a pupil who depicted the elder as a recipient of apocalyptic revelation and a prophet. The danger of ‘secularization’ indicated in 1 John is also evident in the letters to the seven churches. At all events the Apocalypse, too, is to be included in the Johannine Corpus in a broader sense.