A final determination of the amount necessary to correct any previous determination under this section, and any transfer of amounts between the Postal Service and the Department of Defense based on that final determination, shall be made not later than 6 months after the end of fiscal year 2023. (c) Consultation required All estimates and determinations under this section of the amount of postal benefits under this Act used in any period shall be made by the Department of Defense in consultation with the Postal Service. 4. Duration The postal benefits under this Act shall apply with respect to mail matter sent during the period beginning on October 1, 2017, and ending on September 30, 2023.