Rabbi Harav Yaakov Medan (etzion.org.il/en/chapter-12b-daniels-prayer-continued) states: 'According to historical scholarship, the second year of the Persian Darius, when the rebuilding of the Second Temple commenced, was the year 521 B.C.E., and the Second Temple was destroyed in 70 C.E. Thus, according to this system, the Temple stood for 591 years. However, according to a beraita in Seder Olam [which places Creation at 3760 BCE] and the gemara in Bava Batra 4a, the Second Temple stood for only 420 years. Its construction began in the year 3408 and it was destroyed in 3828.' How is this year discrepancy to be explained--an important question for the elucidation of the seventy weeks prophecy of Daniel 9:24-27?*
*'The accepted interpretation in the Talmud (Nazir 32b) and all the commentators is that the "seventy weeks" allude to the 490 years between the destruction of the First Temple and the destruction of the Second Temple. This period includes within it the seventy years of desolation from the destruction of the First Temple until the second year of the reign of Darius (the Persian), when the building of the Second Temple commenced, and the 420 years that the Second Temple stood.' (Medan) In a footnote to this, he says, 'The discrepancy between these two calculations [that of historical scholarship and Seder Olam] is discussed at length in our article and that of C. Chefetz in Megadim 14 on the period of the kings of Persia and Media.' This journal is not accessible to me.