Then the king, when he heard these words, was sore displeased with himself, and set his heart on Daniel to deliver him: and he laboured till the going down of the sun to deliver him.
Then the king ... was sore displeased with himself - for having suffered himself to be entrapped into such a hasty decree (Proverbs 29:20). On the one hand he was pressed by the immutability of the law, fear that the princes might conspire against him, and desire to consult for his own reputation, not to seem fickle; on the other, by regard for Daniel, and a desire to save him from the effects of his own rash decree.
And he laboured until the going down of the sun to deliver him. The king took this time to deliberate, thinking that after sunset Daniel would be spared until morning, and that meanwhile some way of escape would turn up. But (Daniel 6:15) then the conspirators assembled tumultuously-literally, to prevent this delay in the execution, lest the king should meantime change his decree.