The Return as a thief is not related to the Second Coming. The Second Coming can be calculated to the day.
These scriptures make it very clear that Jesus comes as a thief in the night, but no one knows the day or the hour of His return, but that we need to be prepared before Jesus returns.
Mat 24:29 Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
Mat 24:30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory.
Mat 24:31 And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.
Mat 24:36 But of that day and hour knoweth no man, no, not the angels of heaven, but my Father only.
Mat 24:37 But as the days of Noe were, so shall also the coming of the Son of man be.
Mat 24:38 For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noe entered into the ark,
Mat 24:39 And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be.
Mat 24:43 But know this, that if the goodman of the house had known in what watch the thief would come, he would have watched, and would not have suffered his house to be broken up.
Mat 24:44 Therefore be ye also ready: for in such an hour as ye think not the Son of man cometh.
1Thess 5:1 But of the times and the seasons, brethren, ye have no need that I write unto you.
1Thess 5:2 For yourselves know perfectly that the day of the Lord so cometh as a thief in the night.
1Thess 5:3 For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.
Rev 16:15 Behold, I come as a thief. Blessed is he that watcheth, and keepeth his garments, lest he walk naked, and they see his shame.