The last days or end of the days are written in the old testament in different books, It is not written in a sequence but seen sporadically and we have to dig deep to find them. In the old testament in many places written as the Lord's day or day of the Lord.
Isiah 13:6-13 Wail for the day of the LORD is at hand! It will come as destruction from the Almighty. Therefore all hands will be limp, every man's heart will melt, and they will be afraid. Pangs and sorrows will take hold of them; They will be in pain as a woman in childbirth; They will be amazed at one another; Their faces will be like flames. Behold the day of the LORD comes, cruel, with both wrath and fierce anger, to lay the land desolate; And He will destroy its sinners from it. For the stars of heaven and their constellations, will not give their light; The sun will be darkened in its going forth, and the moon will not cause its light to shine.
Daniel 12: 1-4 At that time Michael shall stand up, the great prince who watch over the sons of your people. And there shall be a time of trouble, such as never was since there was a nation even to that time. And at that time your people shall be delivered. Everyone who is found written in the book. And many of those who sleep in the dust of the earth shall awake. Some to everlasting life, some to shame and everlasting contempt. Those who are wise shall shine like the brightness of firmament, and those who turn many to righteousness like the stars forever and ever. " But you, Daniel shut up the words, and seal the book until the time of the end, many shall run to and from and knowledge shall increase."
Some explanation to understand the passage. Michael is the archangel and he guards over Israel and Jewish people. The book of Daniel was not understood for centuries and now people are understanding it better as it is the time of the end.
Daniel 12:9-12 And he said' go your way, Daniel, for the words are closed up and sealed till the time of the end. Many shall be purified, made white, and refined. But the wicked shall do wickedly, and none of the wicked shall understand, but the wise shall understand. And from the time that daily sacrifice is taken away, and the abomination of desolation is set up, there shall be thousand two hundred and ninety days. Blessed is he who waits and comes to one thousand three hundred and thirty days.
Joel 2:1-11 Blow the trumpet in Zion, and sound the alarm in My holy mountain! Let all the inhabitants of the land tremble; for the day of the Lord is coming, for it is at hand: A day of darkness and gloominess, a day of clouds and thick darkness, like the morning clouds spread over the mountains. A people come, great and strong, the like of whom has never been; Nor will there ever be any such after them, even for many successive generations. A fire devours before them, and behind them a flame burns; The land is like the garden of Eden before them, and behind them a desolate wilderness; surely nothing shall escape them. Their appearance is like the appearance of horses; and like swift steeds, so they run with a noise like chariots. Over the mountain tops they leap, devours the stubble, like a strong people set in battle array. Before them the people writhe in pain; All faces are drained of color. THey run like mighty men, they climb the wall like men of war; every one marches in formation, and they do not break ranks. They do not push one another; Everyone marches in his own column. Though they lung between weapons, they are not cut down. They run to and fro in the city, they run on the wall; They climb into the houses, they enter into the houses, they enter at the windows like a thief. The earth quakes before them, the heavens tremble; The sun and the moon grow dark and the stars diminish in their brightness. The LORD gives voice before His army, For His camp is very great; And strong is the One who executes His word. For the day of the LORD is great and terrible and who can endure it?
Joel 2:30-31 And I will show wonders in heaven and in earth; Blood and fire and pillars of smoke. The sun shall be turned into darkness, and the moon into blood, before the coming of the great and awesome day of the LORD.
Amos 5:18-20 Woe to you who desire the day of the LORD! for what good is the day of the LORD to you? it will be darkness and not light. It will be as though a man fled from a lion, and a bear met him or as though he went into the house , leaned his hand on the wall, and a serpent bit him!
Joel 3:12-16 Let all the nations be wakened and come up to the valley of Jehoshaphat. ( Joel 3:1-2)
Zephaniah 1:7 Be silent in the presence of the Lord God; For the day of the LORD is at hand, for the LORD has prepared a sacrifice; He has invited His guests.
Zephaniah 1:14-18 The great day of the LORD is near; it is near and hastens quickly. The noise of the day of the LORD is bitter. The mighty men shall cry out. That day is the day of wrath, a day of trouble and distress, a day of devastation and desolation, a day of darkness and gloominess, a day of clouds and thick darkness. A day of trumpet and alarm, against the fortified cities and against high towers." I will bring bring darkness upon men, and they shall walk like blind men, because they have sinned against the LORD; Their blood shall be poured out like dust, and their flesh like refuse." Neither their silver nor their gold shall be able to deliver them in the day of the LORD's wrath; But the whole land shall be devoured by the fire of His jealousy, for He will make speedy riddance of all those who dwell in the land.
Zephaniah 3:8 Therefore wait for Me" says the LORD until the day I rise up for plunder; My determination is to gather the nations to My assembly of kingdoms, to pour on them My indignation , all My fierce anger; All the earth shall be devoured with fire of My jealousy.
Zechariah 12:2-4 Behold, I will make Jerusalem a cup of drunkenness to all the surrounding people, when they lay siege against Judah and Jerusalem. And it shall happen that day that I will make Jerusalem a very heavy stone for all people; all who heave it away will surely be cut in pieces, though all the nations of the earth gather against it. In that day, I will strike every horse with confusion, and its rider with madness; I will open My eyes on the house of Judah, and will strike every horse of the people with blindness.
Zechariah 12:9 It shall be in that day that I will seek to destroy all nations that come against Jerusalem.
Zechariah 14:1-7 Behold the day of the Lord is coming, and your spoil will be divided in your midst, for I will gather all the nations to battle against Jerusalem. The city shall be taken, their houses rifled, and the women ravished. Half the city will go into captivity, but the remnant of the people shall not be cut off from the city. Then the LORD will go forth and fight against those nations, as He fights in the day of the battle. And in that day His feet will stand on the mount of olives, which faces Jerusalem on the East. And the Mount of Olives will split in to two, from the east to the west, making a very large valley; Half of the mountain shall move toward the north and half of it toward the south. Then you shall flee through My mountain valley, for the mountain valley shall reach Azal, yes you shall flee, as you fled from the earthquake in the days of Uzziah king of Judah. Thus the LORD my God will come; and all the saints with You.It shall come to pass in that day there will be no night; The lights will diminish. It shall be one day which is known to the LORD-neither day or night. But at evening time it will happen that it will be light.
Zechariah 14: 12-13 And this shall be the plague with which the LORD will strike all the people who fought against Jerusalem; Their flesh shall dissolve while they stand on their feet, their eyes shall dissolve in their sockets, and their tongues shall dissolve in their mouths. It shall come to pass in that day,that a great panic from the LORD will be among them. Everyone will seize the hand of his neighbor, and raise his hand against his neighbor's hand;
Malachi 3:2 But who can endure the day of His coming? and who can stand when He appears? For He is like a refiner's fire and like launderer's soap.
These are the verses that shows us how the day of LORD will be, We will continue to look into the new testament and see how Jesus' coming will be.