(a) Section 4 of the Portal Act does not affect the computation of hours worked within the “workday” proper, roughly described as the period “from whistle to whistle,” and its provisions have nothing to do with the compensability under the Fair Labor Standards Act of any activities engaged in by an employee during that period.^[34] Under the provisions of section 4, one of the conditions that must be present before “preliminary” or “postliminary” activities are excluded from hours worked is that they ‘occur either prior to the time on any particular workday at which the employee commences, or subsequent to the time on any particular workday at which he ceases’ the principal activity or activities which he is employed to perform. Accordingly, to the extent that activities engaged in by an employee occur after the employee commences to perform the first principal activity on a particular workday and before he ceases the performance of the last principal activity on a particular workday, the provisions of that section have no application. Periods of time between the commencement of the employee's first principal activity and the completion of his last principal activity on any workday must be included in the computation of hours worked to the same extent as would be required if the Portal Act had not been enacted.^[35] The principles for determining hours worked within the “workday” proper will continue to be those established under the Fair Labor Standards Act without reference to the Portal Act,^[36] which is concerned with this question only as it relates to time spent outside the “workday” in activities of the kind described in section 4.^[37]

(b) “Workday” as used in the Portal Act means, in general, the period between the commencement and completion on the same workday of an employee's principal activity or activities. It includes all time within that period whether or not the employee engages in work throughout all of that period. For example, a rest period or a lunch period is part of the “workday”, and section 4 of the Portal Act therefore plays no part in determining whether such a period, under the particular circumstances presented, is or is not compensable, or whether it should be included in the computation of hours worked.^[38] If an employee is required to report at the actual place of performance of his principal activity at a certain specific time, his “workday” commences at the time he reports there for work in accordance with the employer's requirement, even though through a cause beyond the employee's control, he is not able to commence performance of his productive activities until a later time. In such a situation the time spent waiting for work would be part of the workday,^[39] and section 4 of the Portal Act would not affect its inclusion in hours worked for purposes of the Fair Labor Standards Act.