Generally speaking, California law requires an employer to pay an employee for "standby" time when the employer requires the employee to be at the employer's place of business. As stated in the Labor Commissioner's Enforcement Policies and Interpretations Manual:
Controlled Standby. If the employee’s time is so restricted that they cannot pursue
personal activities and come and go as he pleases, the employer is considered to have
direction and control of the employee. The DLSE has adopted the test which the
California Supreme Court announced in the case of Madera Police Officers Assn. v. City of
Madera (1984) 36 Cal.3d 403, and will apply that test to determine the extent of control.
However, numerous courts have held that California law does not require an employer to compensate an employee for "on call time," even if the employer requires the employee to wear a beeper and report to work in a relatively short period of time.
For a more direct answer to your particular situation, I recommend that you contact an attorney in your area who represents employees in wage and hour cases.
Disclaimer: This answer does not constitute legal advice, and should not be relied on as each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.