It will take understanding.
He spoke these words as Jesus: "No one knows about that day or hour, not even the angels in heaven, nor the Son, but only the Father". But Jesus died and was raised, becoming the Christ, a life-giving Spirit. His nature, then, transcended time and space. For example, while it was not possible to include all believers in Jesus as His body, because He was a singular man with one body, it is now possible to include all believers in Christ.
But let's look at a couple things:
First, what was said is "No one knows..." This is present tense. As in "no one knows at this time". So, who doesn't know, He said no one (man), angels, nor the Son; so even He did not know. He did not know as Jesus. Only the Father knew.
Let's look at something the Holy Spirit revealed to John:
Revelation 1: "This is the revelation of Jesus Christ, which God gave Him to show His servants what must soon come to pass. He made it known by sending His angel to His servant John, who testifies to everything he saw."
So, right away we see that this is the revelation of Jesus Christ given to Him by God. AND THEN, we see that it was given to an angel to give to John.
Jesus said "No one (man) knows, not the angels, not the Son only God. So...
No man > no angel > no Son > only God.
But Revelation 1 reverses the order of Jesus' words. In this instance, Jesus who is now the Christ, gives it to an angel to give to John.
But how did Christ get it? From the Father.
When Jesus addressed His departure, He comforted the disciples with many words.
In John 16 this is recorded:
"He (the Father) will glorify Me, for He will take of what is Mine and declare it to you. All things that the Father has are Mine. Therefore I said that He will take of Mine and declare it to you."
Jesus knew His Father was about to glorify Him with the glory He had in the beginning. He also knew that all the Father had was His inheritance and that He (Jesus) was about to receive all the Father had.
Well, the Father knew the Day. So, Jesus, as the Christ, is about to receive the knowledge of the Day.
So, when He originally spoke "No one knows about that day or hour, not even the angels in heaven, nor the Son, but only the Father" He was telling the truth, He did not know.
But now that He was going to the Father to inherit all the Father had, the revelation of the Day would be given to Him.
So, the original order was no man > no angel > no Son > only God.
But, now from heaven, through an angel, Christ gives the revelation to a man, John.
"This is the revelation of Jesus Christ, which God gave Him to show His servants what must soon come to pass. He made it known by sending His angel to His servant John, who testifies to everything he saw."
God gives to the >Son gives to the angels >gives to man. This is a complete reversal of the order. The circle is complete.
But if that isn't enough, here is 1 Thessalonians 5
"Now about the times and seasons, brothers, we do not need to write to you. For you are fully aware that the Day of the Lord will come like a thief in the night. While people are saying, “Peace and security,” destruction will come upon them suddenly, like labor pains on a pregnant woman, and they will not escape.
But you, brothers, are not in the darkness...
(So he's making a comparison between two camps: those who ARE in darkness and those who ARE NOT in darkness)
..so that this day should overtake you like a thief. For you are all sons of the light and sons of the day; we do not belong to the night or to the darkness. So then, let us not sleep as the others do, but let us remain awake and sober."
We are NOT like those who live in darkness. Therefore, the Day of His return will not overtake us like a thief.
Conclusion: we do not presently know the day but WE WILL KNOW THE DAY. No one will know in enough time to write a book about it or to get rich off of it, but those who remain sober and awake, in the Lord, will not be surprised.