Paul himself knows the dangers of setting dates and times for the coming of the Lord. This passage occurs after the famous 1 Th 4:13-18 passage used as evidence by many proponents of the rapture. This is not our concern. The point isn't what Christ's coming will look like, but that He is coming back. Just as no one knows when a thief will come, no one knows the dates and times the Father has set.
The day of the Lord is directly from the Hebrew yom Yahweh, which describes both a time of God's judgment but also a time of deliverance. We are not called to worry about when Jesus will come back, but to eagerly await his return. Only the unprepared are worried.
Again to belabor the point, just as a pregnant woman knows not the hour she will go into labor, it will fall suddenly on those who do not expect it. We persevere in our preparations because we know the Bridegroom can come at any minute. We do not simply wait and watch and worry, we live. Come, Lord Jesus, come! Let’s celebrate!
 Matthew 24:43 "But understand this: If the owner of the house had known at what time of night the thief was coming, he would have kept watch and would not have let his house be broken into." (Jesus's words)
 Am 5:18-20; Ob 15; Joel 1:15; 2:1f; Zp 1:14-16; Joel 2:31-32; Zc 14:1-21