Section 550.121 - Authorization of night pay differential(a) Except as provided by paragraph (b) of this section, nightwork is regularly scheduled work performed by an employee between the hours of 6 p.m. and 6 a.m. Subject to § 550.122 , and except as otherwise provided in this subpart, an employee who performs nightwork is entitled to pay for that work at his or her rate of basic pay plus a night pay differential amounting to 10 percent of his or her rate of basic pay.(b) The head of a department may designate a time after 6 p.m. and a time before 6 a.m. as the beginning and end, respectively, of nightwork for the purpose of paragraph (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 paragraph (a) of this section. Times so designated as the beginning or end of nightwork shall correspond reasonably with the end or beginning, respectively, of the customary hours of business in the locality.(c) An employee is not entitled to night pay differential while engaged in training, except as provided in § 410.402 of this chapter.33 FR 12458, Sept. 4, 1968, as amended at 48 FR 3934, Jan. 28, 1983; 64 FR 69175, Dec. 10, 1999