Adam Clarke on Psalms 69:13

My prayer is unto thee, O Lord, in an acceptable time - This seems to refer to the end of the captivity, which Jeremiah had said should last seventy years, Jer 25:11, Jer 25:12 : "The whole land shall be a desolation, and an astonishment; and these nations shall serve the king of Babylon seventy years. And it shall come to pass, when seventy years are accomplished, that I will punish the king of Babylon," etc. The conclusion of this period was the accepted tome of which the psalmist speaks. Now, they incessantly pray for the fulfillment of the promise made by Jeremiah: and to hear them, would be the truth of God's salvation; it would show the promise to be true, because the salvation - the deliverance, was granted.