In other works I have pointed to Jer. 18:5-8 as an answer to some Skeptical charges about God "changing his mind":
Then the word of the Lord came to me, saying... "The instant I speak concerning a nation and concerning a kingdom, to pluck up, to pull down, and to destroy it, if that nation against whom I have spoken turns from its evil, I will relent of the disaster that I thought to bring upon it"
The problem? The story starts with Manasseh the son of Hezekiah, who did a lot of the usual bad stuff, including some of the worst idolatry recorded in the OT (2 Kings 21). God announced serious judgment for this (21:10-15), but Manasseh kept on keeping on (21:16), as did his son Amon (who reigned two years) after he died (21:20). Finally Josiah came on the scene and proceeded to clean things up seriously, doing as much good as Manasseh did bad, if not twice as much.
So what's the issue? The Skeptic will say:
One would think, then, that if any nation were ever entitled to have Yahweh "relent" of the disaster he had pronounced upon it, Judah under the reign of Josiah would certainly have qualified. But it didn't. After all the reforms of Josiah had been described in detail, the writer of 2 Kings made this astonishing announcement:
Nevertheless Yahweh did not turn from the fierceness of His great wrath, with which His anger was aroused against Judah, because of all the provocations with which Manasseh had provoked Him. And Yahweh said, "I will also remove Judah from My sight, as I have removed Israel, and will cast off this city Jerusalem which I have chosen, and the house of which I said, `My name shall be there'" (23:26-27).
"From this," we hear, "one can only conclude that it wasn't always true that when Yahweh spoke 'concerning a nation and concerning a kingdom, to pluck up, to pull down, and to destroy it' that he would 'relent of the disaster' that he had thought to bring upon it if the nation turned from its evil."
One might of course make the point that after Josiah died, his son Jehoahaz, and Jeohaikim after him, made another 180 turn; and the punishment did not at least come during Josiah's reign, but only after these two other kings did their worst.
Still, the answer is in the very quote under discussion:
At what instant I shall speak concerning a nation, and concerning a kingdom, to pluck up, and to pull down, and to destroy it; If that nation, against whom I have pronounced, turn from their evil, I will repent of the evil that I thought to do unto them. And at what instant I shall speak concerning a nation, and concerning a kingdom, to build and to plant it...
The terms of Jeremiah are very specific here: at what instant. Manasseh reigned 55 years, Amon 2 more, for a total of 57 years of idolatrous behavior. It isn't specified how many years into Manasseh's reign the warning of 21:11-15 was made, but even if made in year 54 (unlikely), Josiah's turnaround wasn't done "an instant" later as required.
Nineveh in Jonah's time was a lot smarter -- they unpacked the sackcloth and shoveled the ashes in less than a day. The word behind "an instant" is rega', and is used to mean "in the wink of an eye" -- not 3-55 years.
-JPH