EUSEBIUS
http://rbedrosian.com/euseb8.htm
After this, during [the next] 70 years, the Babylonian captivity of the Jews occurred and the destruction of the [temple's] site. According to the Bible, this ended in the second year of King Darius of Persia, which was during the 65th Olympiad [B.C. 520, 519, 518, 517]. …
The captivity lasted for seventy years, and ended in the second year of Darius Hystaspes, who had become king of the Persians, Assyrians, and Egyptians. …
There was a period of 70 years from the destruction of the temple until the second year of Darius. …
At this point one might inquire: Why does it state in the beginning of the book of Ezra [1.1]? …
Furthermore, subsequent [passages] indicate that freedom [was given] to the Jews [at that point] and that it was Cyrus who ordered that the temple be rebuilt. From this one would assume that it was during the time of Cyrus, rather than Darius, that the 70 years of captivity came to an end.
To this I reply that the prophecies refer to two [distinct] 70-year periods.
The first began with the destruction of the temple and ended, as Zechariah stated, in the second year of Darius.
The second extends from the enslavement of the Jews to the capture of Babylon and the destruction of the Chaldean kingdom. This began in the time of the prophecy and ended with Cyrus, as Jeremiah recorded.
[Jeremiah] further predicted [Jeremiah 29.10]. … All this came to a head during the time of Cyrus.
The period of the enslavement [of the Jews] should not be reckoned from the [time of the] destruction of the temple, but earlier—from the second year of [the reign of] Jehoiakim, king of the Jews, when Nebuchadnezzar the king of the Babylonians enslaved them. [It could be reckoned] even earlier, from the time when the prophet Jeremiah first began to prophesy. From that time until the siege [of Jerusalem] and the burning of the temple 40 years elapsed, and 70 years until the first year of Cyrus.
From the start of Jeremiah's prophesying until Cyrus' reign, the first 70 years [period] elapsed.
However, from the destruction of the temple until Cyrus, 30 years elapsed, while it was in the second year of Darius that [the other] 70 years was completed. [The temple] was restored in the eighth year of Darius.