5 U.S.C. § 6129

For purposes of administering sections 6303(a), 6304, 6307(a) and (d), 6323, 6326, 6327, and 8339(m) of this title, in the case of an employee who is in any program under this subchapter, references to a day or workday (or to multiples or parts thereof) contained in such sections shall be considered to be references to 8 hours (or to the respective multiples or parts thereof).