43 C.F.R. § 2.62
When can you expect a decision on your appeal?
(a) The basic time limit for responding to an appeal is 20 workdays after receipt of an appeal meeting the requirements of § 2.59 of this subpart.
(b) If the Department is unable to reach a decision on your appeal within the given time limit for response, the appropriate deciding official for FOIA appeals will notify you of your statutory right to seek review in a United States District Court.