In regards to the endtimes; It is easy to find when the Day of the Lord begins.
Unfortunately, many modern theories and views have misunderstood this; and missed these scriptures; and therefore have placed the start of the Day of the Lord at the wrong time; and created much confusion within eschatological circles in reference to the Day of the Lord.
Jesus, through His infinite wisdom and use of the scriptures; shows us that the Day of the Lord begins at His Second Advent....and in no way before.
Jesus said,
"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: And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory. "
So the faithful bible student can know assuredly, from Jesus' own words; that the sun, moon, and stars will not grow dark until 'after the tribulation' that will culminate in His Glorious 2nd Advent.
Does the Bible anywhere else, tell us when 'The Day of the Lord' will begin; in relation to the darkening of the sun, moon, and stars?
Yes. It tells us that not until after the sun, moon, and stars are darkened, will the Day of the Lord begin.
Isaiah 13:9
"Behold, the day of the LORD cometh, (it hasn't started yet, but will be preceeded by the celestial sign) cruel both with wrath and fierce anger, to lay the land desolate: and he shall destroy the sinners thereof out of it. For the stars of heaven and the constellations thereof shall not give their light: the sun shall be darkened in his going forth, and the moon shall not cause her light to shine."
Also
Again, not until the 2nd Advent; will the celestial signs preceeding the Day of the Lord occur...
Isaiah 24:23
"Then the moon shall be confounded, and the sun ashamed, when the LORD of hosts shall reign in mount Zion, and in Jerusalem, and before his ancients gloriously."
Also, most specifically,
Joel 2:31
"The sun shall be turned into darkness, and the moon into blood, before the great and terrible day of the LORD come."
Paul also, shows the Day of the Lord being directly associated to the Advent of our Lord.
II Thessalonians 4:15
"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. 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: 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. Wherefore comfort one another with these words. But of the times and the seasons, brethren, ye have no need that I write unto you. For yourselves know perfectly that the day of the Lord so cometh as a thief in the night. For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape. But ye, brethren, are not in darkness, that that day should overtake you as a thief. Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness. "
We even find in Revelation; further commitment that not until the Lord's Advent; will the Day of the Lord begin....
Revelation 16:14
"which go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty. Behold, I come as a thief. Blessed is he that watcheth, and keepeth his garments, lest he walk naked, and they see his shame. And he gathered them together into a place called in the Hebrew tongue Armageddon."
God's Word alone, makes it abundantly clear that the endtime start to the Day of the Lord will be preceeded by the darkening of the sun, moon, and stars; and will be acompanied by the glorious 2nd Advent of our Lord.
Any view that attempts to teach the Day of the Lord beginning prior to what Scripture plainly teaches; should be avoided.