20 CFR 218.10: When a supplemental annuity begins.

An employee supplemental annuity begins on the latest of—

(a) The beginning date of the employee age or disability annuity;

(b) The first day of the month in which the employee meets the age and years of service requirements as shown in part 216 of this chapter; or

(c) The first day of the twelfth month before the month in which the employee disability annuitant under age 65 gives up the right to return to work as explained in part 216 of this chapter.