29 CFR 784.115: Exempt and noncovered work performed during the workweek.

The wage and hours requirements of the Act do not apply to any employees during any workweek in which a portion of his activities falls within section 13(a)(5) if no part of the remainder of his activities is covered by the Act. Similarly, the overtime requirements are inapplicable in any workweek in which a portion of an employee's activities falls within section 13(b)(4) if no part of the remainder of his activities is covered by the Act. Covered activities for purposes of the above statements mean engagement in commerce, or in the production of goods for commerce, or in an occupation closely related or directly essential to such production or employment in an enterprise engaged in commerce or in the production of goods for commerce, as explained in §§ 784.17 through 784.19.