Do we include holiday hours when calculating the OT Rate for subcontractors?

I am trying to clear up this issue. We are the prime contractor and have several companies that provide labor for us as a subcontractor. I know that when the subcontractor is paying their employees, they are required to include holiday hours in the base for computing their OT rate. My question is are we required to include holiday hours in what the subcontractor bills us, or do they have to work 40 billable hours before we start paying them their OT rate? As an example, in a week with a holiday, if a subcontractor's employee works 35 hours, would we be responsible for paying the subcontractor 32 hours at the straight time rate and 3 hours at the overtime rate, or since they only have 35 billable hours, would we pay the subcontactor 35 hours at the straight time rate? Thanks so much!