The mark and the image of the fifth seal will serve to distinguish between those who remain faithful to God and those who worship the man of sin. Once everyone has made their choice and that initial segregation is completed, the sixth seal is opened.
I looked when He broke the sixth seal, and there was a great earthquake; and the sun became black as sackcloth made of hair, and the whole moon became like blood; and the stars of the sky fell to the earth, as a fig tree casts its unripe figs when shaken by a great wind. The sky was split apart like a scroll when it is rolled up, and every mountain and island were moved out of their places. Then the kings of the earth and the great men and the commanders and the rich and the strong and every slave and free man hid themselves in the caves and among the rocks of the mountains; and they said to the mountains and to the rocks, “Fall on us and hide us from the presence of Him who sits on the throne, and from the wrath of the Lamb; for the great day of their wrath has come, and who is able to stand?” Revelation 6:12-17 NASB
According to Jesus, the events of the sixth seal indicate the end of the time of great tribulation of the saints. Both Daniel 7:25 and Revelation 13:5 talk about a war against the saints that lasts for forty-two months. The time of great tribulation takes place at the beginning of that forty-two-month war.
“For then there will be a great tribulation, such as has not occurred since the beginning of the world until now, nor ever will. Unless those days had been cut short, no life would have been saved; but for the sake of the elect those days will be cut short.”
“But immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light, and the stars will fall from the sky, and the powers of the heavens will be shaken. And then the sign of the Son of Man will appear in the sky." Matthew 24:21-22, 29-30a NASB
The opening of the sixth seal is when God intervenes and cuts short the days of great tribulation. The people of the world will not be able to persecute believers with the same intensity as they had been able to previously. The forty-two-month war against the saints will continue on and last for that full duration. That’s not what gets cut short. It’s the intensity of the persecution that began those forty-two months that gets cut short because those who aligned themselves with the man of sin will be dealing with the effects of plagues that are introduced with the opening of the next seal.