If neither the angels in heaven nor the Son of Man Himself as man know the appointed time, how is it possible for it to be known among men? From the words of the Saviour it is understood only that we must be ever vigilant and mindful of our salvation, ever ready for the coming of the Lord, for we know neither the day nor the hour of His coming, nor even the hour of our own end in this life. His appearance will be unexpected, as the Lord forewarned us when he said, Watch therefore, for ye know neither the day nor the hour wherein the Son of Man cometh. (Mat. 25:13)
[…]
The true Church teaches, equally with the Apostle Paul, that the day of the Lord will come as a thief in the night and that no one knows the day nor the hour in which the Son of Man will come.

It is possible only for the approach of the Second Coming to be known by the signs which must come before:

~ The preaching of the Gospel throughout the world. (Mat. 24:15)

~ The turn of the Jews to Christianity after the preaching of the Gospel in the entire world. (Rom. 11:25-34)

~ The appearance of the Antichrist, also called the man of iniquity or the beast, together with his representatives, pseudo-Christs, false prophets, and every type of false wonder worked by the power of Satan in order to deceive the people. The Antichrist will sit in the place of God acting as if he were God and as an unrelenting beast he will pursue with all rage and furore the chosen servants of God. (1 Jn. 2:18; 2 Thess. 2:3-11; Rev. 13:1-8, 20:1-10; Mat. 24:9)

~ The multiplication of wickedness and the growing cold of love between men, hatred and betrayal of one another. (Mat. 24:10-12)

~ A torrent of bloodshed, wars and rumours of wars between nations, people and states. (Mat. 24:6-7)

~ The appearance of calamities such as mass starvation, sicknesses etc. (Mat. 24:7-9)

~ The appearance of certain signs in the world such as the darkening of the sun and moon, the falling of stars from the sky, the passing away of heaven and earth.

~ The appearance in the heavens of the sign of the Son of Man, the True Cross, because this is the sign of victory of our Lord and no other sign so alerts us of His imminent arrival as does His Cross.