I'm doing 2021 and 2022 returns for a client.   They have overpayment from 2021 which they want applied to 2022 to cover tax liability but does result in a small refund.    How long do I need to wait after efiling the 2021 return before efiling the 2022 return to assure the 2021 overpayment has been applied.   Client would like to get the 2022 refund yet this year but I'm leery of sending too soon and making a mess of the applied overpayment situation.   With IRS shutdown only days away I'm not sure it can all happen this year.

TIA for your advice.