((a)) An agency head may waive or delay the completion of some or all of the requirements of by publishing in the Federal Register, not later than the date of publication of the final rule, a written finding, with reasons therefor, that the final rule is being promulgated in response to an emergency that makes compliance or timely compliance with the provisions of impracticable.

((b)) Except as provided in section 605(b), an agency head may not waive the requirements of . An agency head may delay the completion of the requirements of for a period of not more than one hundred and eighty days after the date of publication in the Federal Register of a final rule by publishing in the Federal Register, not later than such date of publication, a written finding, with reasons therefor, that the final rule is being promulgated in response to an emergency that makes timely compliance with the provisions of impracticable. If the agency has not prepared a final regulatory analysis pursuant to within one hundred and eighty days from the date of publication of the final rule, such rule shall lapse and have no effect. Such rule shall not be repromulgated until a final regulatory flexibility analysis has been completed by the agency.