Whenever in the opinion of the Administrator a modification of an existing standard for naval stores is necessary in the interest of the trade, he shall announce a hearing thereon, to be held not less than 6 months subsequent to such announcement. Notice of the hearing stating the terms or description of the proposed modification of any standard, or a summary thereof, shall be given by publication in the Federal Register and by such other means as may be practicable. The hearing shall be conducted by an official designated by the Administrator, and reasonable opportunity shall be afforded to all interested persons to present their views, arguments and data, verbally or in writing, in favor of or in opposition to the proposed modification. All relevant material presented at said hearing, or a summary thereof, and a recommendation as to adoption or rejection of the proposed modification shall be transmitted to the Administrator for his consideration. A modified standard established and promulgated by the Administrator shall become effective not less than 6 months after the promulgation thereof.