Okla. Admin. Code § 715:10-5-11
Credit for military service may be purchased and is limited to a maximum of five (5) years. This includes service both before and after July 1, 1943. No credit may be given for any year of military duty which duplicates any other credit already granted or in which a year of creditable service is available for service in the public schools of Oklahoma. The member must have two (2) years of creditable Oklahoma service after the years of military service credit for each year to be purchased. Out-of-state service credit cannot be counted as employment in obtaining military service credit. The purchase of military service must be completed, and payment made to TRS, no later than 90 days prior to the effective date of a member's official retirement date.
Okla. Admin. Code § 715:10-5-11