Cal. Civ. Code § 9

All other days than those mentioned in Section 7 are business days for all purposes; provided, that as to any act appointed by law or contract, or in any other way, to be performed by, at, or through any bank organized under the laws of or doing business in this state, any optional bank holiday as defined in Section 7.1 is not a business day; and provided, that any act appointed by law or contract, or in any other way, to be performed on any day which is an optional bank holiday as defined in Section 7.1, by, at, or through any bank or branch or office thereof, whether acting in its own behalf or in any other capacity whatsoever, may be performed on that optional bank holiday if the bank or branch or office by, at, or through which the act is to be performed is open for the transaction of business on that optional bank holiday, or, at the option of the person obligated to perform the act, it may be performed on the next succeeding business day.