Cal. Government Code § 19170

(a) The board shall establish the length of the probationary period for each class to be six months, unless the board establishes a longer period of not more than one year. The probationary period commences on the first day the employee reports to work or begins performing the job duties. (b) By rule, the board may: (1) Increase the length of individual probationary periods by adding periods of time to any periods of time an employee, while serving as a probationer, is absent from the employee’s position. (2) Require an additional probationary period not to exceed the length of the probationary period of the class in which the probationer was appointed when the probationary employee returns after an extended period of absence and the remainder of the probationary period is insufficient to evaluate the probationary employee’s current performance. (c) Upon written agreement between an appointing power and an employee who alleges they have a disability, as defined in Section 12926, subject to approval of the agreement by the board, the employee’s probationary period may be extended for a period, not to exceed six months, to allow the appointing power to provide a reasonable accommodation to the employee and the employee to demonstrate, before the probationary period ends, the ability to perform satisfactorily the essential functions of the position with reasonable accommodation. Nothing in this subdivision may relieve an appointing power from complying with applicable law requiring reasonable accommodation or prohibiting discrimination based on disability, and no employee, as a condition of an agreement to extend the probationary period, may be required to waive or release any rights they may have under applicable law requiring reasonable accommodation or prohibiting discrimination based on disability.