California Code, Education Code - EDC § 24005

(a) A disability allowance under this part shall become effective upon any date designated by the member, provided all of the following conditions are met:

(b) If the member is employed to perform creditable service subject to coverage under the Defined Benefit Program at the time the disability allowance is approved under this part, the member shall notify the system in writing, within 90 days, of the last day on which the member will perform service. If the member does not respond within 90 days, or if the last day on which service will be performed is more than 90 days after the date the system notifies the member of approval of the disability allowance, the member's application for a disability allowance shall be rejected and a disability allowance shall not be payable to the member.