Notwithstanding sections 6103 and 6104 of this title, if any employee on a flexible schedule under section 6122 of this title is relieved or prevented from working on a day designated as a holiday by Federal statute or Executive order, such employee is entitled to pay with respect to that day for 8 hours (or, in the case of a part-time employee, an appropriate portion of the employee's biweekly basic work requirement as determined under regulations prescribed by the Office of Personnel Management).