Charles Ellicott Commentary Zechariah 1:12

"Then the angel of Jehovah answered and said, O Jehovah of hosts, how long wilt thou not have mercy on Jerusalem and on the cities of Judah, against which thou hast had indignation these threescore and ten years?" — Zechariah 1:12 (ASV)

Consequently, the angel of the Lord intercedes for Jerusalem and the cities of Judah.

These threescore and ten years. —This is an old English expression. The Hebrew has one word—seventy—which is often used as a round number.

From the taking of Jerusalem by Nebuchadnezzar (B.C. 605-6) to the date of the decree of Cyrus for the return of the Jews (B.C. 538) is sixty-eight years. These are the seventy years of captivity foretold by Jeremiah (Jeremiah 25:11; Jeremiah 29:10).

But eighteen years had now elapsed since that decree of Cyrus. Consequently, the angelic intercessor, in saying how long ... these seventy years, can hardly have referred to the seventy years spoken of by Jeremiah, since the actual number of years was now eighty-eight.

Therefore, it is most probable that the reference is to the period of sixty-eight years between the second taking of Jerusalem by Nebuchadnezzar, when Zedekiah was removed in chains to Babylon (B.C. 588), and the year of this prophecy (B.C. 520).