California Code, Education Code - EDC § 45308

(b)(1) For purposes of this section, in school districts with an average daily attendance below 250,000 for service commencing or continuing after July 1, 1971, “length of service” means all hours in paid status, whether during the school year, a holiday, recess, or during any period that a school is in session or closed, but does not include any hours compensated solely on an overtime basis as provided for in Section 45128.  Nothing in this section shall preclude the governing board of a school district from entering into an agreement with the exclusive representative of the classified employees that defines “length of service” to mean the hire date.  For purposes of this section, in school districts with an average daily attendance of 250,000 or more, for service commencing or continuing after January 1, 1986, “length of service” shall be determined by the date of hire.

(2) If a governing board enters into an agreement with the exclusive representative of classified employees that defines “length of service” to mean the hire date, the governing board may define “length of service” to mean the hire date for a classification of employee not represented by any exclusive bargaining unit.