Question: How long was the period between the First and Second Temples?
Answer: Cyrus gave the Jews permission to return to their land and rebuild the Temple in the first year of his reign, which was about 50 years after Nebuchadnezzar destroyed the First Temple. But because of opposition from the Samaritans, the Second Temple wasn’t completed until about 20 years later, 70 years after the destruction of the First Temple. Daniel (9:2) says that the land was desolate for 70 years, but the 70 years either began before the destruction of the first Temple, or ended after the return. Rashi on Daniel 9:2 says that the 70 years began when Nebuchadnezzar subjugated Yehoyakim, which was at least 20 years before the Temple was destroyed. 2 Chron. 36:21-22 says that a 70-year period ended when Cyrus became king; but the commentators (e.g., Rashi) take this as referring to a 490-year period in which the Jews failed to observe 70 Sabbatical years, and the total of 490 years includes only 52 years after the destruction of the First Temple.
All the Best,
Rabbi Azriel Schreiber