The general rule that the unit of time to be used in determining the
application of the exemption to an employee is the workweek (see
Overnight Motor Transportation Co. v. Missel, 316 U.S. 572; Mitchell v.
Stinson, 217 F. 2d 210; Mitchell v. Hunt. 263 F. 2d 913; Puerto Rico
Tobacco Marketing Co-op. Ass'n. v. McComb, 181 F. 2d 697). Thus, the
workweek is the unit of time to be taken as the standard in determining
the applicability to an employee of section 13(a)(5) or section 13(b)(4)
(Mitchell v. Stinson, supra). An employee's workweek is a fixed and
regularly recurring period of 168 hours--seven consecutive 24-hour
periods. It may begin at an hour of any day set by the employer and need
not coincide with the calendar week. Once the workweek has been set it
commences each succeeding week on the same day and at the same hour.
Changing the workweek for the purpose of escaping the requirements of
the Act is not permitted. If in any workweek an employee does only
exempt work he is exempt from the wage and hours provisions of the Act
during that workweek, irrespective of the nature of his work in any
other workweek or workweeks. An employee may thus be exempt in one
workweek and
not the next (see Mitchell v. Stinson, supra). But the burden of
effecting segregation between exempt and nonexempt work as between
particular workweeks is on the employer (see Tobin v. Blue Channel
Corp., 198 F. 2d 245).
