29 C.F.R. § 785.7

The United States Supreme Court originally stated that employees subject to the act must be paid for all time spent in “physical or mental exertion (whether burdensome or not) controlled or required by the employer and pursued necessarily and primarily for the benefit of the employer and his business.” (Tennessee Coal, Iron & Railroad Co. v. Muscoda Local No. 123, 321 U. S. 590 (1944)) Subsequently, the Court ruled that there need be no exertion at all and that all hours are hours worked which the employee is required to give his employer, that “an employer, if he chooses, may hire a man to do nothing, or to do nothing but wait for something to happen. Refraining from other activity often is a factor of instant readiness to serve, and idleness plays a part in all employments in a stand-by capacity. Readiness to serve may be hired, quite as much as service itself, and time spent lying in wait for threats to the safety of the employer's property may be treated by the parties as a benefit to the employer.” (Armour & Co. v. Wantock, 323 U.S. 126 (1944); Skidmore v. Swift, 323 U.S. 134 (1944)) The workweek ordinarily includes “all the time during which an employee is necessarily required to be on the employer's premises, on duty or at a prescribed work place”. (Anderson v. Mt. Clemens Pottery Co., 328 U.S. 680 (1946)) The Portal-to-Portal Act did not change the rule except to provide an exception for preliminary and postliminary activities. See § 785.34.