California Code, Business and Professions Code - BPC § 732

(1) If the patient requests a refund, within 30 days following the request from that patient for a refund if the duplicate payment has been received, or within 30 days of receipt of the duplicate payment if the duplicate payment has not been received.

(2) If the patient does not request a refund, within 90 days of the date the physician and surgeon or dentist knows, or should have known, of the receipt of the duplicate payment, the physician and surgeon or dentist shall notify the patient of the duplicate payment, and the duplicate payment shall be refunded within 30 days unless the patient requests that a credit balance be retained.