29 CFR 548.501: Overtime hours based on nonstatutory standards.

Many employees are paid daily overtime pay or Saturday overtime pay or overtime pay on a basis other than the statutory standard of overtime pay required by section 7(a) of the Act. In these cases, the number of hours for which an employee is paid at least one and one-half times an established basic rate must equal or exceed the number of hours worked in excess of the applicable number of hours established in section 7(a) of the Act in the workweek. However, only overtime hours under the employment agreement which also qualify as overtime hours under section 7(e) (5), (6), or (7) of the Act 25 may be offset against the hours of work in excess of the applicable number of hours established in section 7(a) of the Act.