'Three Days' in the Bible

Then said the king to Amasa, Assemble me the men of Judah within three days, and be thou here present.

So Gad came to David, and told him, and said unto him, Shall seven years of famine come unto thee in thy land? or wilt thou flee three months before thine enemies, while they pursue thee? or that there be three days' pestilence in thy land? now advise, and see what answer I shall return to him that sent me.