29 C.F.R. § 785.9

(a) The Portal-to-Portal Act. The Portal-to-Portal Act (secs. 1-13, 61 Stat. 84-89, 29 U.S.C. 251-262) eliminates from working time certain travel and walking time and other similar “preliminary” and “postliminary” activities performed “prior” or “subsequent” to the “workday” that are not made compensable by contract, custom, or practice. It should be noted that “preliminary” activities do not include “principal” activities. See §§ 790.6 to 790.8 of this chapter. The use of an employer's vehicle for travel by an employee and activities that are incidental to the use of such vehicle for commuting are not considered “principal” activities when meeting the following conditions: The use of the employer's vehicle for travel is within the normal commuting area for the employer's business or establishment and the use of the employer's vehicle is subject to an agreement on the part of the employer and the employee or the representative of such employee. Section 4 of the Portal-to-Portal Act does not affect the computation of hours worked within the “workday”. “Workday” in general, means the period between “the time on any particular workday at which such employee commences (his) principal activity or activities” and “the time on any particular workday at which he ceases such principal activity or activities.” The “workday” may thus be longer than the employee's scheduled shift, hours, tour of duty, or time on the production line. Also, its duration may vary from day to day depending upon when the employee commences or ceases his “principal” activities. With respect to time spent in any “preliminary” or “postliminary” activity compensable by contract, custom, or practice, the Portal-to-Portal Act requires that such time must also be counted for purposes of the Fair Labor Standards Act. There are, however, limitations on this requirement. The “preliminary” or “postliminary” activity in question must be engaged in during the portion of the day with respect to which it is made compensable by the contract, custom, or practice. Also, only the amount of time allowed by the contract or under the custom or practice is required to be counted. If, for example, the time allowed is 15 minutes but the activity takes 25 minutes, the time to be added to other working time would be limited to 15 minutes. (Galvin v. National Biscuit Co., 82 F. Supp. 535 (S.D.N.Y. 1949) appeal dismissed, 177 F. 2d 963 (C.A. 2, 1949))

(b) Section 3(o) of the Fair Labor Standards Act. Section 3(o) gives statutory effect, as explained in § 785.26, to the exclusion from measured working time of certain clothes-changing and washing time at the beginning or the end of the workday by the parties to collective bargaining agreements.