Jamieson, Fausset and Brown on Jeremiah 25:11

11. seventy years--(Jr 27:7). The exact number of years of Sabbaths in four hundred ninety years, the period from Saul to the Babylonian captivity; righteous retribution for their violation of the Sabbath (Le 26:34, 35; 2Ch 36:21). The seventy years probably begin from the fourth year of Jehoiakim, when Jerusalem was first captured, and many captives, as well as the treasures of the temple, were carried away; they end with the first year of Cyrus, who, on taking Babylon, issued an edict for the restoration of the Jews (Ezr 1:1). Daniel's seventy prophetic weeks are based on the seventy years of the captivity (compare Da 9:2, 24).