Albert Barnes Commentary Jeremiah 29:10

"For thus saith Jehovah, After seventy years are accomplished for Babylon, I will visit you, and perform my good word toward you, in causing you to return to this place." — Jeremiah 29:10 (ASV)

After seventy years - literally, according to the measure of the fulfillment of 70 years for Babylon. The 70 years (Jeremiah 25:11 note) are primarily the length of the Babylonian empire, and only in a secondary sense that of the Jewish exile.