Accordingly, an employer who fails to take such activities into account in paying compensation to an employee who is subject to the Fair Labor Standards Act is not protected from liability or punishment in either of the following situations.
In applying these principles, it should be kept in mind that under the provisions of section 4(c) of the Portal-to-Portal Act, "preliminary" or "postliminary" activities which take place outside the workday "before the morning whistle" or "after the evening whistle" are, for purposes of the statute, not to be considered compensable by a contract, custom or practice if such contract, custom or practice makes them compensable only during some other portion of the day.
Conference Report, pp. 12, 13. See also § 790.12 .
29 C.F.R. §790.4