14 days after your Retro Afterpay order is created. You can see the dates that you need to pay your Retro Afterpay order in both the Afterpay app and the Money by Afterpay app at any time by clicking on the Retro'd transaction.
Refer to here for further information.
As part of the ramp down of Money by Afterpay, Retro as a service will only be available within the app until the 25 September 2022