'Three Days' in the Bible

Then the king said to Amasa, "Call the men of Judah together for me in three days, and you be present here with them too."

Gad went to David and told him, "Shall seven years of famine come upon your land? Or shall you flee for three months from your enemy with him in hot pursuit? Or shall there be three days of plague in your land? Now decide what I should tell the one who sent me."