5 CFR § 842.303 - General.
(1) Except as provided in paragraph (a)(2) of this section, no service credit is allowed for a period of separation from service.
(2) Service credit is allowed for a period of separation of less than 4 days and for a period of separation during which an individual was receiving benefits under subchapter I of chapter 81 of title 5, United States Code, provided the individual returns to duty in the Government subject to FERS.
(b) Service credit cannot be granted in excess of actual calendar time from the date of appointment to the date of separation from service.
(c) Any period of time for which service credit under chapter 84 of title 5, United States Code, is specifically allowed by a provision of law is creditable under this subpart subject to any applicable deposit requirements.