Nothing herein contained shall be construed to prevent or invalidate the entry, issuance, service, or execution of any writ, summons, confession of judgment, or other legal process whatever, on any of the holidays or half holidays herein designated as holidays; nor to prevent any banking institution from keeping its doors open or transacting its business, on any Saturday afternoon, if by a vote of its directors it shall elect to do so, unless such Saturday is appointed as a bank holiday under the provisions of this act: And provided further, That any banking institution may, by a vote of its directors, or in the case of a private bank by action of the private banker or bankers, notice of which shall have been posted in its banking house for not less than fifteen days before the taking effect thereof, observe any Saturday throughout the year as a full holiday with like effect hereunder as though such day had been designated as a full holiday by the provisions of this act, and may in the same manner, observe as a full holiday any Monday next following the first day of January, or the twenty-fifth day of December whenever any of such holidays shall occur on a Saturday with like effect hereunder as though such day had been designated as a full holiday by the provisions of this act.