5 U.S.C. § 5545: Night, standby, irregular, and hazardous duty differential

periods of absence with pay during these hours due to holidays; and periods of leave with pay during these hours if the periods of leave with pay during a pay period total less than 8 hours. The head of an agency may designate a time after 6:00 p.m. and a time before 6:00 a.m. as the beginning and end, respectively, of nightwork for the purpose of subsection (a) of this section, at a post outside the United States where the customary hours of business extend into the hours of nightwork provided by subsection (a) of this section. an employee in a position requiring him regularly to remain at, or within the confines of, his station during longer than ordinary periods of duty, a substantial part of which consists of remaining in a standby status rather than performing work, shall receive premium pay for this duty on an annual basis instead of premium pay provided by other provisions of this subchapter, except for irregular, unscheduled overtime duty in excess of his regularly scheduled weekly tour. Premium pay under this paragraph is determined as an appropriate percentage, not in excess of 25 percent, of such part of the rate of basic pay for the position as does not exceed the minimum rate of basic pay for GS–10 (including any applicable locality-based comparability payment under section 5304 or similar provision of law and any applicable special rate of pay under section 5305 or similar provision of law) (or, for a position described in section 5542(a)(3) of this title , of the basic pay of the position), by taking into consideration the number of hours of actual work required in the position, the number of hours required in a standby status at or within the confines of the station, the extent to which the duties of the position are made more onerous by night, Sunday, or holiday work, or by being extended over periods of more than 40 hours a week, and other relevant factors; or an employee in a position in which the hours of duty cannot be controlled administratively, and which requires substantial amounts of irregular, unscheduled overtime duty with the employee generally being responsible for recognizing, without supervision, circumstances which require the employee to remain on duty, shall receive premium pay for this duty on an annual basis instead of premium pay provided by other provisions of this subchapter, except for regularly scheduled overtime, night, and Sunday duty, and for holiday duty. Premium pay under this paragraph is an appropriate percentage, not less than 10 percent nor more than 25 percent, of the rate of basic pay for the position, as determined by taking into consideration the frequency and duration of irregular, unscheduled overtime duty required in the position. an employee in an occupational series covering positions for which the primary duties involve the prevention, control, suppression, or management of wildland fires, as determined by the Office; and in such other circumstances as the Office may by regulation prescribe; and may not exceed an amount equal to 25 percent of the rate of basic pay applicable to the employee.