'Three Days' in the Bible

Then the king said to Amasa, "Summon for me the men of Judah [within] three days, {and be here yourself}."

Then Gad came to David, and he told him and said to him, "Shall seven years of famine in the land come to you? Or three months of your fleeing from your enemies while he [is] pursuing you? Or should there be three days of pestilence in your land? Now consider and decide what I must return to the one who sent me a word."