The earliest church fathers, after the destruction of Jerusalem/Temple in 70AD, still looked toward Jesus' Second Coming.
Therefore, my children, in six days, that is, in six thousand years, all things will be finished. “And He rested on the seventh day.” This meaneth: when His Son, coming [again], shall destroy the time of the wicked man,1662 and judge the ungodly, and change the sun, and the moon,1663 and the stars, then shall He truly rest on the seventh day.
Barnabas Chapter XV
[in discussing two advents] But the rest of the prophecy shall be fulfilled at His second coming.
Dialogue with Trypho Chapter CX, Justin Martyr
Wherefore He shall, at His second coming, first rouse from their sleep all persons of this description, and shall raise them up, as well as the rest who shall be judged, and give them a place in His kingdom.
Against Heresies Book IV Chapter XXII, Irenaeus
Ver. 23. “He who denies the Son,” by ignoring Him, “has not the Father, nor does he know Him.” But he who knoweth the Son and the Father, knows according to knowledge, and when the Lord shall be manifested at His second advent, shall have confidence and not be confounded. Which confusion is heavy punishment.
Clement of Alexandria Book VIII Chapter III
Now these signs of degradation quite suit His first coming, just as the tokens of His majesty do His second advent, when He shall no longer remain “a stone of stumbling and a rock of offence,” but after His rejection become “the chief corner-stone,” accepted and elevated to the top place3189 of the temple, even His church, being that very stone in Daniel, cut out of the mountain, which was to smite and crush the image of the secular kingdom.3190 Of this advent the same prophet says: “Behold, one like the Son of man came with the clouds of heaven, and came to the Ancient of days; and they brought Him before Him, and there was given Him dominion and glory, and a kingdom, that all people, nations, and languages should serve Him. His dominion is an everlasting dominion, which shall not pass away; and His kingdom that which shall not be destroyed.”
Against Marcion Book III Chapter VII, Tertullian
This is He who, although He was silent in His passion, yet by and by will not be silent in His vengeance. This is our God, that is, not the God of all, but of the faithful and believing; and He, when He shall come manifest in His second advent, will not be silent.
Cyprian Treatise IX Chapter 23
In short, based on scripture, they distinguished two advents. They knew the first had taken place 30AD, the Temple destroyed 40 years later in 70AD, and Christ's Second Advent was still future.