HMRC have updated their guidance Check the last dates for deferment period adjustments in customs declaration service and CHIEF that shows the last dates for late item input and adjustments to the customs handling of import and export freight (CHIEF) deferment periods.
The March 2023 to February 2024 dates have been added.
https://www.gov.uk/government/publications/chief-last-dates-for-adjustments-to-deferment-periods