20 C.F.R. § 1002.115
Is the employee required to report to or submit a timely application for reemployment to his or her pre-service employer upon completing the period of service in the uniformed services?
Yes. Upon completing service in the uniformed services, the employee must notify the pre-service employer of his or her intent to return to the employment position by either reporting to work or submitting a timely application for reemployment. Whether the employee is required to report to work or submit a timely application for reemployment depends upon the length of service, as follows:
(a) Period of service less than 31 days or for a period of any length for the purpose of a fitness examination. If the period of service in the uniformed services was less than 31 days, or the employee was absent from a position of employment for a period of any length for the purpose of an examination to determine his or her fitness to perform service, the employee must report back to the employer not later than the beginning of the first full regularly-scheduled work period on the first full calendar day following the completion of the period of service, and the expiration of eight hours after a period allowing for safe transportation from the place of that service to the employee's residence. For example, if the employee completes a period of service and travel home, arriving at ten o'clock in the evening, he or she cannot be required to report to the employer until the beginning of the next full regularly-scheduled work period that begins at least eight hours after arriving home, i.e., no earlier than six o'clock the next morning. If it is impossible or unreasonable for the employee to report within such time period through no fault of his or her own, he or she must report to the employer as soon as possible after the expiration of the eight-hour period.
(b) Period of service more than 30 days but less than 181 days. If the employee's period of service in the uniformed services was for more than 30 days but less than 181 days, he or she must submit an application for reemployment (written or verbal) with the employer not later than 14 days after completing service. If it is impossible or unreasonable for the employee to apply within 14 days through no fault of his or her own, he or she must submit the application not later than the next full calendar day after it becomes possible to do so.
(c) Period of service more than 180 days. If the employee's period of service in the uniformed services was for more than 180 days, he or she must submit an application for reemployment (written or verbal) not later than 90 days after completing service.