In their letter to Lobsto regarding the neo-Babylonian chronology, the WTS wrote the following regarding the early Church Fathers:
Less than 200 years after Josephus, several early church writers clearly accepted that the length of the desolation or exile was 70 years, and no one gives any other length for this event.
For instance, Tatian the Assyrian (110 to 172 C.E.) in his Address of Hatian to the Greeks, chapter 36;
Clement of Alexandria (153 to 193 C.E.) in his work The Stromata, Book I, chapter 21; and
Irenaeus (120 to 202 C.E.) in Irenaeus Against Heresies, Book III, chapter 21, 2; Book IV, chapter 34, 4, all wrote that the Jews were exiled in Babylon for 70 years.
So did the ancient chronologer Julius Africanus (200 to 232 C.E.) in the Extant Fragments of the Five Books of the Chronography of Julius Africanus, chapter 13, 2.
Thus, while these ancient writers may not have been fully accurate in all the particulars, they do all agree on one point, namely, that the Jews were in captivity for 70 years, and some of these indicate that Jerusalem was desolate for the entire period.
The following shows what each of the Church Fathers wrote at the references that the WTS provided.