I see I did the late Canon Farrar a disservice (by neglecting to quote the title of his book), so let me first correct that oversight.
The citation should read (“Mercy and Judgment”, pages 189-190.)
The following quotes are from Saint Gregory of Nyssa (and note the last, where he speaks of an “aionian interval.”)
We certainly believe, both because of the prevailing opinion, and still more of Scripture teaching, that there exists another world of beings besides, divested of such bodies as ours are, who are opposed to that which is good and are capable of hurting the lives of men, having by an act of will lapsed from the nobler view, and by this revolt from goodness personified in themselves the contrary principle; and this world is what, some say, the Apostle adds to the number of the “things under the earth,” signifying in that passage that when evil shall have been some day annihilated in the long revolutions of the ages, nothing shall be left outside the world of goodness, but that even from those evil spirits shall rise in harmony the confession of Christ’s Lordship.
(On the Soul and the Resurrection)
For it is now as with those who for their cure are subjected to the knife and the cautery; they are angry with the doctors, and wince with the pain of the incision; but if recovery of health be the result of this treatment, and the pain of the cautery passes away, they will feel grateful to those who have wrought this cure upon them. In like manner, when, after long periods of time, the evil of our nature, which now is mixed up with it and has grown with its growth, has been expelled, and when there has been a restoration of those who are now lying in sin to their primal state, a harmony of thanksgiving will arise from all creation, as well from those who in the process of the purgation have suffered chastisement, as from those who needed not any purgation at all. These and the like benefits the great mystery of the Divine incarnation bestows. For in those points in which He was mingled with humanity, passing as He did through all the accidents proper to human nature, such as birth, rearing, growing up, and advancing even to the taste of death, He accomplished all the results before mentioned, freeing both man from evil, and healing even the introducer of evil himself. For the chastisement, however painful, of moral disease is a healing of its weakness.
(The Great Catechism, ch. XXVI)
…agony will be measured by the amount of evil there is in each individual. For it would not be reasonable to think that the man who has remained so long as we have supposed in evil known to be forbidden, and the man who has fallen only into moderate sins, should be tortured to the same amount in the judgment upon their vicious habit; but according to the quantity of material will be the longer or shorter time that that agonizing flame will be burning; that is, as long as there is fuel to feed it. In the case of the man who has acquired a heavy weight of material, the consuming fire must necessarily be very searching; but where that which the fire has to feed upon has spread less far, there the penetrating fierceness of the punishment is mitigated, so far as the subject itself, in the amount of its evil, is diminished. In any and every case evil must be removed out of existence, so that, as we said above, the absolutely non-existent should cease to be at all. Since it is not in its nature that evil should exist outside the will, does it not follow that when it shall be that every will rests in God, evil will be reduced to complete annihilation, owing to no receptacle being left for it? But, said I, what help can one find in this devout hope, when one considers the greatness of the evil in undergoing torture even for a single year; and if that intolerable anguish be prolonged for an aionian interval, what grain of comfort is left from any subsequent expectation to him whose purgation is thus commensurate with an entire age?
(On the Soul and the Resurrection)
As for the Latin Fathers, Jerome translated Micah 4:5 (in the Latin Vulgate) as follows:
quia omnes populi ambulabunt unusquisque in nomine dei sui nos autem ambulabimus in nomine Domini Dei nostri in aeternum et ultra (i.e. aeternum and “further”, or “beyond”.)