'Three Days' in the Bible

Now the king said to Amasa [the commander of his army], “Summon the [fighting] men of Judah to me within three days, and be present here yourself.”

So Gad came to David and told him, and said to him, “Shall seven years of famine come to you in your land? Or will you flee three months before your enemies as they pursue you? Or shall there be three days of pestilence (plague) in your land? Now consider this and decide what answer I shall return to Him who sent me.”