Garry you asked and I did my best. Jeanne
God has instructed us to watch even though Jesus said we would not know the day or the hour of his return. Signs were given us to watch for. Genesis 1:14 “And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:” Luke 21:36 “Watch ye therefore, and pray always, that ye may be accounted worthy to escape all these things that shall come to pass, and to stand before the Son of man.”
In the past God gave man 120 (Jubilee years of 6000) years. Genesis 6:3 “And the Lord said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.” So where did he start this count? Was it when Adam sinned or when man began to build the tower at Babel to reach Heaven?
God gave the prophecy of 70 years for Judah in Babylon. Jeremiah 25:11-12 “And this whole land shall be a desolation, and an astonishment; and these nations shall serve the king of Babylon seventy years. And it shall come to pass, when seventy years are accomplished, that I will punish the king of Babylon, and that nation, saith the Lord, for their iniquity, and the land of the Chaldeans, and will make it perpetual desolations.
Before that God told Moses the Israelites would wander in the desert for 40 years. Numbers 14:34 “After the number of the days in which ye searched the land, even forty days, each day for a year, shall ye bear your iniquities, even forty years, and ye shall know my breach of promise.”
This last one of 390 years: From Solomon 2984/1016 BC +390=3374/626BC is the year Nebuchadnezzar is said to be born. He is the one in his 19th year  began his siege of Jerusalem. Ezekiel 4:5-6 “For I have laid upon thee the years of their iniquity, according to the number of the days, three hundred and ninety days [390 years]: so shalt thou bear the iniquity of the house of Israel. And when thou hast accomplished them, lie again on thy right side, and thou shalt bear the iniquity of the house of Judah forty days [40 years]: I have appointed thee each day for a year.”
The kingdom of Israel was divided in 3024/976 BC in the Northern Kingdom of Israel and the Southern Kingdom of Judah. So when did the 40 years apply to the Southern Kingdom of Judah? I believe it was 40 years after Jesus was resurrected and the Holy Spirit descended on the 120 believers at Pentecost plus 40 years when the Temple was burned on the 9th of Av. I have a date for that but it is speculative. Some say 70 AD and many parrot that date.Remember God gave an exact date for the foundation of the first Temple by Solomon, for the second Temple, also the exact date for the foundation of the Third Temple, which is not a building of bricks and stones. Zech. 4:6 “Not by might, nor by power, but by my spirit, saith the Lord of hosts.” John 18:36 “My kingdom is not of this world: if my kingdom were of this world, then would my servants fight, that I should not be delivered to the Jews: but now is my kingdom not from hence.” Haggai 2:18-21 “Consider now from this day and upward, from the 24th day of the ninth month [Kislev 24], even from the day that the foundation of the Lord's temple was laid, consider it. Is the [promised] seed yet in the barn? yea, as yet the vine, and the fig tree, and the pomegranate, and the olive tree, hath not brought forth: from this day will I bless you.” Luke 4:21 “he began to say unto them, ‘This day is this scripture fulfilled in your ears’.”Jesus was the Promised Seed to Abraham