Unofficially, it varies. Scripture says Jonah was inside the whale "for ever", but that only lasted 3 days. The catch here is that if forever means a literally endless span of non-time, as the Pharisees contend, then Mercy lasts every bit as long as the popular Endless Torment that so many of them are enamored with. How the Prince of Peace can find a way to cook billions of lost souls (damned from before birth, per Psalm 58) and still claim that His Mercy endures endlessly is no small tangle of contradictory xmas lights.