Cal. Commercial Code § 3304

(a) An instrument payable on demand becomes overdue at the earliest of the following times: (1) On the day after the day demand for payment is duly made. (2) If the instrument is a check, 90 days after its date. (3) If the instrument is not a check, when the instrument has been outstanding for a period of time after its date which is unreasonably long under the circumstances of the particular case in light of the nature of the instrument and usage of the trade. (b) With respect to an instrument payable at a definite time the following rules apply: (1) If the principal is payable in installments and a due date has not been accelerated, the instrument becomes overdue upon default under the instrument for nonpayment of an installment, and the instrument remains overdue until the default is cured. (2) If the principal is not payable in installments and the due date has not been accelerated, the instrument becomes overdue on the day after the due date. (3) If a due date with respect to principal has been accelerated, the instrument becomes overdue on the day after the accelerated due date. (c) Unless the due date of principal has been accelerated, an instrument does not become overdue if there is default in payment of interest but no default in payment of principal.