IRS Processing and Payout Timeline for Payroll Tax Offset
Generally, you can expect to receive payment approximately 6 - 8 weeks after you have filed your respective quarterly payroll tax filing. For example, if you filed the R&D credit in your payroll filings on time for Q3, then you should expect to receive payment by the end of Q4.
Keep in mind the timing is dependent upon how quickly the IRS can work through the filings and process payments, so timing is subject to change. If your credit is greater than one quarter's worth of payroll tax, most payroll systems will require you to refile Form 8974 each quarter until your R&D credit is fully exhausted. In the event that your R&D credit benefit is greater than the relevant amount of payroll taxes, any unused portion of the credit is carried forward to subsequent quarters. In such a case, you may end up filing Form 8974 multiple times, depending on how many quarters it takes you to fully utilize the credit.