The commissioner of banking and consumer finance may, from time to time, adopt and promulgate rules regulating banking hours, and such rules shall have all the force and effect of law. In addition thereto, the commissioner may permit a bank to close its doors for business at such time or times during the week as the commissioner determines will not prevent the rendering of proper and reasonable banking service to the community and trade area in which the bank is located. The commissioner shall not authorize any bank to close for more than one whole day during any week, state and federal legal holidays and Sundays excepted; provided, however, that in the event any state or federal legal holiday shall fall on a Saturday, then the commissioner may permit banks to observe the preceding Friday as a legal holiday, or if such holiday shall fall on Sunday, then the commissioner may permit banks to observe the next following Monday as a legal holiday.