Heidegger's Bible Handbook: 1 John: Time of Writing
6. It appears to have been written quite late, after most of the New Testament books.
The time of writing is not well established. Nevertheless, it is probable that it was written late, after the other Scriptures of the New Testament, but before the second and third Epistles and the Apocalypse. His words in 1 John 2:18 appear to argue this: Παιδία, ἐσχάτη ὥρα ἐστί, little children, it is the last hour; and, as ye have heard that Antichrist cometh, even now have there been many Antichrists. Therefore, John wrote in the last years of the Apostolic preaching, and with heretics discreetly springing up after the truth preached, and with Antichrists corrupting the truth.