The last chapter of Revelation records Jesus saying three times that His return will be with “quickness” (tachu). This is the best translation of this Greek word to English. The angel also says those things revealed to John and Jesus’ servants will happen “quickly” (vs.6). The angel uses the same stem of the Greek word: takei.
The Greek word tachu is used only 12 times in the New Testament and every time the best rendering to English is “quickly” or “suddenly.” The English word tachometer indicates an instrument measuring speed and is derived from this Greek term. So the three repeated statements in the last chapter of the bible is telling us the nature of His return: it will be speedily when He does return. The second advent will be sudden and not gradual.
The disciples asked the resurrected Christ when He will restore The Kingdom to Israel (Acts 1.7). Jesus clearly told them that the timing was not theirs to know but was solely the prerogative of the Father. So, the Patmos vision given to John in Rev. 22 did not change this mystery. It is still the Father’s prerogative to set the duration of the age. Jesus will return the second time to save His people and he will do it suddenly and without delay when the time is right. He was not telling John that the return will happen shortly time-wise.
So those who mock the bible and think Jesus promised to return “soon” and now a long time has passed, they think he was wrong, mock in ignorance. Jesus, as clear as possible, said His return would be suddenly and dramatic (and universal from other statements). Yes, many early Christians thought Jesus would return in their lifetimes but they were mistaken more probably from enthusiasm than what the text said.