'Seventy Years' in the Bible

Then the messenger of Yahweh responded, and said, O Yahweh of hosts! How long wilt, thou, not have compassion upon Jerusalem, and the cities of Judah, - against which thou hast had indignation these seventy years?

Speak thou unto all the people of the land, and unto the priests, saying, - When ye fasted and lamented in the fifth and in the seventh, even these seventy years, did ye, really fast, unto, me?