Adam Clarke on 2 Samuel 18:10

I saw Absalom hanged in an oak - He must have hung there a considerable time. this man saw him hanging; how long he had been hanging before he saw him, we cannot tell. He came and informed Joab; this must have taken up a considerable time. Joab went and pierced him through with three darts; this must have taken up still more time. It is therefore natural to conclude that his life must have been nearly gone after having been so long suspended, and probably was past recovery, even if Joab had taken him down.