29 C.F.R. § 1620.24
In applying the various tests of equality to the requirements for the performance of particular jobs, it is necessary to scrutinize each job as a whole and to look at the characteristics of the jobs being compared over a full work cycle. For the purpose of such a comparison, the appropriate work cycle to be determined would be that performed by members of the lower paid sex and a comparison then made with job duties performed by members of the higher paid sex during a similar work cycle. The appropriate work cycle will be determined by an examination of the facts of each situation. For example, where men and women custodial workers in a school system perform equal work during the academic year, but the men perform additional duties in the summer months, the appropriate work cycle for EPA purposes would be the academic year. In that instance, the additional summer duties would not preclude the application of the equal pay standard or justify the higher wage rate for men for the period when the work was equal.
29 C.F.R. § 1620.24