The Apocalypse expresses the fervent waiting for the end within the circles in which the writer lived--not an expectation that will happen at some unknown point x in time, but one in the immediate present. If we browse through the writings of that period we observe that this expectation of the end continued. In fact, we also find the writing of the first half of the second century sufficient evidence to indicate that the expectation of the Parousia was by no means at an end then.
At the end of the Didache ("the teaching of the twelve apostles"), from the time shortly after 100, there is, for example, an apocalyptic chapter, which corresponds completely in its outline to the Synoptic apocalypse in Mark 13 (and the parallel chapters in the other Synoptic Gospels.) Here we can only very cautiously say that it used the same words, but that its content is imperceptible in the process of change. It is quite similar to the Epistle of Barnabas, which was written a little later than the Didache, where we read: (The day is near in which everything will perish together with the evil. The Lord and His recompense are near).
Again and again the old expressions echo. They echo apparently almost unchanged, but ("doubt about the imminence of the Lord’s return is increasingly mixed with them until around the middle of the second century, when the Shepherd of Hermas thinks he has found a solution and expresses it with great thoroughness and emphasis: the Parousia-the Lord’s return-has been postponed for the sake of Christians themselves. The building of the tower has not been stopped,) it is only temporarily suspended. Therefore and this is the warning of the Shepherd of Hermas, on account of which the entire work was really written, do good works for your purification, for if you delay too long, the construction of the tower may be finished and you will not be included as stones built into it.
The thought of a postponement of the Parousia appears all through 2 Clement but here it is expressly mentioned for the first time. Thus, about the middle of the second century, a decisive turning point occurs, one which can be compared in significance to all other great turning points, including the Reformation. Obviously, we cannot fix this turning point precisely at the year 150, for it took a while until the thought caught hold everywhere. But a development does begin with the Shepherd of Hermas which could not be stopped-a development at the end of which we stand today. As soon as the thought of a postponement of the Parousia was uttered once and indeed not only incidentally, but thoroughly presented in an entire writing-it developed its (own life and power).
At first, people looked at it as only a brief postponement, as the Shepherd of Hermas clearly expresses. But soon, as the end of the world did not occur, it was conceived of as a longer and longer period, until finally-this is today’s situation nothing but the thought of a postponement exists in people’s consciousness. (Kurt Aland. A History of Christianity. (2 vols.) Fortress Press: 1985. Vol. 1,pp.89-102