A credit union shall post its hours of operation prominently in its office. Each credit union shall be open for business during its posted hours, except that a credit union may close: On any State holiday; and At any other time if: Notice of the closing is posted prominently in its office 3 business days in advance; Specifically authorized to close by the Commissioner; or An emergency exists that affects the credit union and it is not practical to obtain authorization from the Commissioner before closing the affected credit union. If a credit union closes under the provisions of subsection (b)(2)(iii) of this section, the chairman of the board or the president of the affected credit union shall notify the Commissioner of the reason for the closing of the credit union as soon as possible but no later than 24 hours after the closing of the credit union.