Answer
According to Ezra 1:1, Cyrus issued the edict to rebuild the temple in the "first" year of his reign. Cyrus actually reigned over the Persians from 559 to 530 B.C., but the year of this proclamation was the first year after his kingdom became the dominant one in the political neighborhood, the first year after he defeated Babylon (cf. 2 Chr. 36:20). Cyrus conquered Babylon in 539 B.C., so the "first" year of Cyrus' reign calculated on this basis would have begun in 538 B.C.
Ezra 3:8 tell us that work on the temple was begun in the second year after the people began to return to Jerusalem for the purpose of rebuilding the temple, which would have been 536 B.C. Ezra 6:17, in turn, informs us that the temple was completed on the third day of the month of Adar (the twelfth month of the Jewish calendar) in the sixth year of the reign of Darius. Darius reigned from 522 B.C. to 486 B.C., so the sixth year of his reign would have been 516 B.C.
Thus, work on the second temple was begun in 536 B.C. and completed in 516 B.C. It took about twenty years to build.
Answer by Ra McLaughlin
Ra McLaughlin is Vice President of Finance and Administration at Third Millennium Ministries.