Future prophecy (Imminent) / Signs Appearing Now
Jesus disciples came to him and asked him that question after he told them that he would leave them and return. Jesus gives them signs to watch for leading to the end. I believe this to be the end of the age, which is now the current church age. Jesus goes on to tell his disciples that the day and hour is not known.
He is speaking of the rapture of the church. He gives an example (Matthew 24:40-41) of two men in the field, one taken one left, two women grinding, one taken and one left. He goes on to speak of his coming like a thief in the night (Matthew 24:42-44). This must be the rapture, we will not know when he is coming. It will be as the days of Noah, it will also be at the coming of the Son of Man. I also take this to mean that wickedness will abound, as well as the people will be living their lives as normal, not watching or listening to the signs around them.
The second coming of Christ is a different time. When he returns to earth, we all will know. There will be signs (Luke 21).