The board of each bank and of each trust company shall hold a meeting not less than once each calendar quarter. Regular meetings of the board shall be held within this state. Any regular or special meeting is valid wherever held if held upon written consent of all members of the board given either before or after the meeting and filed with the secretary of the corporation. Special meetings of the board may be held upon four days’ notice by mail, unless the articles or bylaws provide

otherwise, or 24 hours’ notice delivered personally or by telephone or by telegraph, unless the articles or bylaws provide for a shorter period.