'Three Days' in the Bible

Then said the king to Amasa, "Call me the men of Judah together within three days and present thyself here."

And Gad came to David and showed him and said unto him, "Whether wilt thou have seven years hunger in thy land, or that thou flee three months before thine enemies and they following thee, or that there be three days pestilence in thy land? Now understand, and see what word I shall bring again to him that sent me."