Auto loan: If the SCRA effective date is immediately after the first payment due date, but the first payment was never made, what loan term is used to calculate the new payment amount?

Example: Loan date 8/1/2020, First payment Due 9/1/2020 (never made), SCRA date 9/5/2020. If the original loan term is 72 months, and the balance has not changed because no payment has been made, is the new SCRA loan term 72 months or 71 months?

My initial thought is that 72 payments are still owed, plus the interest accrued at the contract rate from loan date to SCRA date. If the original repayment schedule is 72 payments, wouldn't 72 payments need to be made to roll due dates and reach maturity?

As of 9/5/20, you drop the interest rate. That has no impact on the amount of the first payment that was due. Your remaining 71 payment would be calculated through a re-amortization of the loan as if the first payment was made as planned.