California Business And Professions Code Section 2456.1

All osteopathic physician`s and surgeon`s certificates shall expire at 12 midnight on the last day of the birth month of the licensee during the second year of a two-year term if not renewed on or before that day. The board shall establish by regulation procedures for the administration of a birth date renewal program, including, but not limited to, the establishment of a system of staggered license expiration dates such that a relatively equal number of licenses expire monthly. To renew an unexpired license, the licensee shall, on or before the dates on which it would otherwise expire, apply for renewal on a form prescribed by the board and pay the prescribed renewal fee.