Since you don't seem to think the "Day of the Lord" and the days of great tribulation will happen at the same time, please delineate for us, in Revelation, WHERE: what verses to what verses:
1. The Day of the Lord...beginning
2. The days of great tribualtion: beginning and ending
I take the day of the Lord to be involving the 7 last vials of wrath. Let's look at one or two of those.
Revelation 16:2 And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men which had the mark of the beast, and upon them which worshipped his image
Revelation 16:10 And the fifth angel poured out his vial upon the seat of the beast; and his kingdom was full of darkness; and they gnawed their tongues for pain,
11 And blasphemed the God of heaven because of their pains and their sores, and repented not of their deeds.
Let's compare the above to some of the following in Revelation 13.
Revelation 13:4 And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?
5 And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months.
Revelation 13:11 And I beheld another beast coming up out of the earth; and he had two horns like a lamb, and he spake as a dragon.
12 And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.
13 And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
14 And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.
15 And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
Does it sound reasonable that any of the above would be taking place while any of the vials of wrath were going on at the time?
For instance---
And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth---And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men which had the mark of the beast, and upon them which worshipped his image
What seems more reasonable? The former occurs first followed by at a later time, the latter. Or both occur at the same time? If you agree the former sounds more reasonable, and the fact we know the beast reigns for 42 months, it should be safe to conclude that the first vial follows after the 42 months have been fulfilled. This in turn agrees with Matthew 24:29.
Matthew 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 :
Though not everyone agrees, most do agree that the tribulation of those days is meaning this same 42 months in Revelation 13. The text indicates that something follows immediately after this 42 months. What I have underlined above is apparently meaning the last 7 vials of wrath. Notice that it says shall the sun be darkened. Compare that to 5th vial, for instance---and his kingdom was full of darkness; and they gnawed their tongues for pain.
We know that is likely meaning literal darkness based on a similar event recorded in the OT.
Exodus 10:21 And the LORD said unto Moses, Stretch out thine hand toward heaven, that there may be darkness over the land of Egypt, even darkness which may be felt.
Notice that it says---even darkness which may be felt. Compare that with the 5th vial----and they gnawed their tongues for pain.
Lets now look at Zephaniah again.
Zephaniah 1:14 The great day of the LORD is near, it is near, and hasteth greatly, even the voice of the day of the LORD: the mighty man shall cry there bitterly.
15 That day is a day of wrath, a day of trouble and distress, a day of wasteness and desolation, a day of darkness and gloominess, a day of clouds and thick darkness,
The text indicates it is a day of darkness. Since I myself take the day of the Lord to be meaning an era of time rather than a single 24 hour day, that means it's not involving only a literal 24 hour day, but is involving many days. How many days, that I'm uncertain about. Though maybe it has something to do with the 1290 and 1335 days in Daniel 12? We know the 42 months in Revelation 13 are 1260 days. 1335 days are 75 more days than 1260 days. So I'm thinking then, though not certain, maybe these extra days are for the last 7 vials?
So when does Matthew 24:29 indicate the sun shall be darkened? During the GT or after the GT? After of course. That then also places the time of the day of the Lord recorded in Zephaniah to be meaning after the GT as well.
1 Thessalonians 5:2 For yourselves know perfectly that the day of the Lord so cometh as a thief in the night
1 Thessalonians 5:9 For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ,
Verse 2 above establishes the context of verse 9. The wrath in verse 9 is not meaning the GT, the wrath in verse 9 is meaning the day of the Lord, and as I illustrated above, the day of the Lord follows after the GT rather than occurring simultaneously with it instead.
If you grasped my point above in regards to the darkness during the 5th vial, being darkness that can be felt, does it seem reasonable that that would be taking place any time during the 42 months recorded in Revelation 13? The point being, there are two wraths involved. The wrath of the GT, and the wrath of the Lord. The former involves satan's wrath. It is mainly the saints whom the wrath is being unleashed upon during the 42 months. The following for one proves it----And it was given unto him to make war with the saints, and to overcome them. If that doesn't involve wrath, what does it involve? And doesn't Revelation 12 indicate satan has come down with great wrath? How could that great wrath not involve this 42 months in Revelation 13, the GT?
Since this post is already rather lengthy, I guess I better make my final point. That being, since there are two periods of wrath, one being satan's, the other being the Lord's, satan is allotted his time, this same 42 months, then it's the Lord's time for His wrath, which involve the 7 last vials after the 42 months have been fulfilled.