If an employee separates for disability retirement after June 30, 1997, and, on the date of separation, the employee—

(a) Satisfies the age and service requirements for optional retirement, the Federal Benefit Payment commences immediately, that is, the Federal Benefit Payment is calculated as though the employee retired under optional retirement rules using only service through June 30, 1997 (See examples 7A and 7B of appendix A of this subpart); or

(b) Does not satisfy the age and service requirements for optional retirement, the Federal Benefit Payment begins when the disability retiree reaches deferred retirement age. (See § 29.343.)