49 C.F.R. § 520.33
To the maximum extent practicable, no administrative action (i.e., any proposed action to be taken by the agency other than agency proposals for legislation to Congress, budget proposals, or agency reports on legislation) subject to this part and covered by an environmental impact statement shall be taken sooner than 90 days after a DEIS has been circulated for comment, furnished to the CEQ, and made public. Neither shall such administrative action be taken sooner than 30 days after the FEIS (together with comments) has been filed with CEQ, and made available to commenting agencies and the public. If the FEIS is filed within 90 days after a DEIS has been circulated for comment, furnished to the CEQ and made public, the 30-day period and 90-day period may run concurrently to the extent that they overlap. The 90-day time period is measured from the date of publication in the FEDERAL REGISTER of the list of weekly filings of environmental impact statements with the CEQ, but the 30-day period is computed from the date of receipt by the CEQ.
49 C.F.R. §520.33