The last trumpet, the beginning of the last judgement.

[Xeno.of.athens]

Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality. So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory.
1 Corinthians 15:51-54 KJV

This is the way the scriptures say it shall be, a single event, a sudden event, not an invisible presence, nor a additional dispensation; just the sounding of the trumpet of God and the change of the corrupt into incorruptible for the faithful.

 

[BobRyan]

The Bible describes that one event just as you say - as a visible single event for His appearing. 1 Cor 15 has it that way
Matt 24
1 Cor 15
Rev 19
1 Thess 4:13-18
2 Thess 1:5-8

all describe the same event - the appearing of Christ. Sudden and visible and catastrophic (in one of its meanings).

1 Cor 15:
In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality. So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory.
1 Corinthians 15:51-54 KJV

Matt 24
29 “Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. 30 Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. 31 And He will send His angels with a great sound of a trumpet, and they will gather together His elect from the four winds, from one end of heaven to the other.


John 14:1-3
“Let not your heart be troubled; you believe in God, believe also in Me. 2 In My Father’s house are many mansions; if it were not so, I would have told you. I go to prepare a place for you. 3 And if I go and prepare a place for you, I will come again and receive you to Myself; that where I am, there you may be also. 4 And where I go you know, and the way you know.”

1 Thess 4:
13 But I do not want you to be ignorant, brethren, concerning those who have fallen asleep, lest you sorrow as others who have no hope. 14 For if we believe that Jesus died and rose again, even so God will bring with Him those who sleep in Jesus.
15 For this we say to you by the word of the Lord, that we who are alive and remain until the coming of the Lord will by no means precede those who are asleep. 16 For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first. 17 Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord. 18 Therefore comfort one another with these words.

2 Thess 1:
6 since it is a righteous thing with God to repay with tribulation those who trouble you, 7 and to give you who are troubled rest with us when the Lord Jesus is revealed from heaven with His mighty angels, 8 in flaming fire taking vengeance on those who do not know God, and on those who do not obey the gospel of our Lord Jesus Christ. 9 These shall be punished with everlasting destruction from the presence of the Lord and from the glory of His power, 10 when He comes, in that Day, to be glorified in His saints and to be admired among all those who believe, because our testimony among you was believed.

 

[BobRyan]

And what triggers that event?

Gospel evangelism and great tribulation

Matt 24;
13 But he who endures to the end shall be saved. 14 And this gospel of the kingdom will be preached in all the world as a witness to all the nations, and then the end will come.

15 “Therefore when you see the ‘abomination of desolation,’ spoken of by Daniel the prophet, standing in the holy place” (whoever reads, let him understand), 16 “then let those who are in Judea flee to the mountains. 17 Let him who is on the housetop not go down to take anything out of his house. 18 And let him who is in the field not go back to get his clothes. 19 But woe to those who are pregnant and to those who are nursing babies in those days! 20 And pray that your flight may not be in winter or on the Sabbath. 21 For then there will be great tribulation, such as has not been since the beginning of the world until this time, no, nor ever shall be. 22 And unless those days were shortened, no flesh would be saved; but for the elect’s sake those days will be shortened.

23 “Then if anyone says to you, ‘Look, here is the Christ!’ or ‘There!’ do not believe it. 24 For false christs and false prophets will rise and show great signs and wonders to deceive, if possible, even the elect. 25 See, I have told you beforehand.

26 “Therefore if they say to you, ‘Look, He is in the desert!’ do not go out; or ‘Look, He is in the inner rooms!’ do not believe it. 27 For as the lightning comes from the east and flashes to the west, so also will the coming of the Son of Man be. 28 For wherever the carcass is, there the eagles will be gathered together.

=====================

Dan 7 -- Judgment completes then tribulation completes then the appearing of Christ

9 “I watched till thrones were put in place,
And the Ancient of Days was seated;
His garment was white as snow,
And the hair of His head was like pure wool.
His throne was a fiery flame,
Its wheels a burning fire;
10 A fiery stream issued
And came forth from before Him.
A thousand thousands ministered to Him;
Ten thousand times ten thousand stood before Him.
The court was seated,
And the books were opened.

11 “I watched then because of the sound of the pompous words which the horn was speaking; I watched till the beast was slain, and its body destroyed and given to the burning flame. 12 As for the rest of the beasts, they had their dominion taken away, yet their lives were prolonged for a season and a time.


13 “I was watching in the night visions,
And behold, One like the Son of Man,
Coming with the clouds of heaven!
He came to the Ancient of Days,
And they brought Him near before Him.
14 Then to Him was given dominion and glory and a kingdom,
That all peoples, nations, and languages should serve Him.
His dominion is an everlasting dominion,
Which shall not pass away,
And His kingdom the one
Which shall not be destroyed.

Daniel’s Visions Interpreted​

15 “I, Daniel, was grieved in my spirit within my body, and the visions of my head troubled me. 16 I came near to one of those who stood by, and asked him the truth of all this. So he told me and made known to me the interpretation of these things: 17 ‘Those great beasts, which are four, are four kings which arise out of the earth. 18 But the saints of the Most High shall receive the kingdom, and possess the kingdom forever, even forever and ever.’


19 “Then I wished to know the truth about the fourth beast, which was different from all the others, exceedingly dreadful, with its teeth of iron and its nails of bronze, which devoured, broke in pieces, and trampled the residue with its feet; 20 and the ten horns that were on its head, and the other horn which came up, before which three fell, namely, that horn which had eyes and a mouth which spoke pompous words, whose appearance was greater than his fellows.


21 “I was watching; and the same horn was making war against the saints, and prevailing against them, 22 until the Ancient of Days came, and a judgment was made in favor of the saints of the Most High, and the time came for the saints to possess the kingdom.

23 “Thus he said:

‘The fourth beast shall be
A fourth kingdom on earth,
Which shall be different from all other kingdoms,
And shall devour the whole earth,
Trample it and break it in pieces.
24 The ten horns are ten kings
Who shall arise from this kingdom.
And another shall rise after them;
He shall be different from the first ones,
And shall subdue three kings.
25 He shall speak pompous words against the Most High,
Shall persecute the saints of the Most High,
And shall intend to change times and law.
Then the saints shall be given into his handFor a time and times and half a time. (42 months, = 1260 literal years)

26 ‘But the court shall be seated,
And they shall take away his dominion,
To consume and destroy it forever.
27 Then the kingdom and dominion,
And the greatness of the kingdoms under the whole heaven,
Shall be given to the people, the saints of the Most High.
His kingdom is an everlasting kingdom,
And all dominions shall serve and obey Him.’