The resurrection/rapture is at His coming just as 1Cor 15:23 states:
1 Corinthians 15:23-24 (KJV) 23 But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming. 24 Then [cometh] the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power.
The Mystery Paul speaks of in 1 Cor 15:51 is the same mystery in Rev 10:7.
1 Corinthians 15:51-52 (KJV) 51 Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, 52 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.
Revelation 10:7 (KJV) But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets.
The last trump is the seventh trump.
Further, Paul explicitly states the dead rise before those whom are alive. He says this TWICE in a span of two sentences in 1 Thess 4:15-16. Which is also the same “coming” in 1 Cor 15:23.
1 Thessalonians 4:15-17 (KJV) 15 For this we say unto you by the word of the Lord, that we which are alive [and] remain unto the coming of the Lord shall not prevent them which are asleep. 16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: 17 Then we which are alive [and] remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
Those whom are alive cannot precede those whom are dead. Period. Scripture is crystal clear.
Pretribulation “rapture” is a lie and easily defeated with scripture.