I am reading under Reg CC: If substantially all business functions are open then it is a banking day. The only thing that is not operational is the work processing.
As Ken said the two definitions work together.
(f)
Banking day means that part of any business day on which an office of a bank is open to the public for carrying on substantially all of its banking functions.
(g) Business day means a calendar day other than a Saturday or a Sunday, January 1, the third Monday in January, the third Monday in February, the last Monday in May, July 4, the first Monday in September, the second Monday in October, November 11, the fourth Thursday in November, or December 25. If January 1, July 4, November 11, or December 25 fall on a Sunday, the next Monday is not a business day.