The vision takes place before the conquest of Babylon. It is in the third year of the reign of Belzhazzar.
But the Ram is already standing and is already dominant in the starting events of the vision itself. This fits the same 457 B.C. start point that Daniel 9 gives it.
Dan 8:4 -
4 no
other beasts could stand against him nor was there anyone to rescue from his power, but he did as he pleased and made himself great --- Persia is dominant at the start of the vision.
"The
first Persian Empire, founded by
Cyrus the Great around
550 B.C., became one of the largest empires in history,"
But This vs 4 is not the start of the Persian empire - rather it at a point where no one can stand against it and it is dominant. And so "it just so happens" that 457 B.C. fits that start and it "just so happens" that it is also the start of the 490 years of Dan 9.
Dan 8 - ends without explanation for the start date
27 Then I, Daniel, was exhausted and sick for days. Then I got up
again and carried on the king’s business; but I was astounded at the vision,
and there was none to explain it.
Dan 9 gives the start event (missing in Dan 8 and given in Dan 9) in the Persian empire that starts both the 70 weeks and the vision in Dan 8
22 He gave
me instruction and talked with me and said, “O Daniel, I have now come forth to give you insight with understanding. 23 At the beginning of your supplications the command was issued, and I have come to tell
you, for you are highly esteemed; so give heed to the message and
gain understanding of the vision. (refers back to the vision of Dan 8)
24 “Seventy weeks have been decreed for your people and your holy city, to finish the transgression, to make an end of sin, to make atonement for iniquity, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy
place. 25 So you are to know and discern
that from the issuing of a decree to restore and rebuild Jerusalem until Messiah the Prince
there will be seven weeks and sixty-two weeks; it will be built again, with plaza and moat, even in times of distress.
So then it
starts in 457 B.C. https://adventistbiblicalresearch.org/wp-content/uploads/70weeks457BC.pdf
Ezra 6 -
Three part decree
14 And the elders of the Jews were successful in building through the prophesying of Haggai the prophet and Zechariah the son of Iddo. And they finished building according to the command of the God of Israel and
the decree of Cyrus, Darius, and Artaxerxes king of Persia. 15 This temple was completed on the third day of the month Adar; it was the sixth year of the reign of King Darius.
Ezra 7 -
takes effect in Jerusalem in 7th year of
Artaxerxes.
6 This Ezra went up from Babylon, and he was a scribe skilled in the law of Moses, which the Lord God of Israel had given;
and the king granted him all he requested because the hand of the Lord his God
was upon him. 7 Some of the sons of Israel and some of the priests, the Levites, the singers, the gatekeepers and the temple servants
went up to Jerusalem in the seventh year of King Artaxerxes.
8
He came to Jerusalem in the fifth month, which was in the seventh year of the king. 9 For on the first of the first month he began to go up from Babylon; and on the first of the fifth month he came to Jerusalem
The text of the 3rd part (in 457 B.C.) of the 3-part decree is given Ezra 7:12-26
"If we use the Persian-Babylonian calendar the date would be 458 B.C.; but if we employ the Jewish calendar the date would be 457 B.C. The Persiancalendar was based on a spring-to-spring civil yearwhile the Jews used a fall-to-fall one.
...
"We are fortunate to have two biblical passagesin the book of Nehemiah that provide an answer tothat question. In Nehemiah 1:1 the arrival of Hananito Susa is dated “in the month of Kislev of the twen-tieth year” of Artaxerxes. Later we are told thatNehemiah spoke to the king about the situation inJerusalem “in the month of Nisan in the twentiethyear of King Artaxerxes” (2:1). The year is the samebut the months are different.
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In any case the 2300 years then ends in 1844. Pushing it back 93 years to a 550 B.C. start would mean that the 2300 years ended around 1747 which is not very useful given that this is before the 1260 years of dark ages persecution in Dan 7 ended. (And it is hard to see how a 1747 end date fits anything you have proposed).