; and (B) such covered veteran shall be presumed to have been exposed to toxic substances at Karshi Khanabad Air Base, Uzbekistan, at any time during the period beginning October 1, 2001, and ending December 31, 2005, unless there is conclusive evidence to establish that— (i) the covered veteran was not exposed to toxic substances in the course of such service in the Armed Forces; or (ii) the illness first became manifest prior to the covered veteran’s exposure. (4) Submission Upon the date on which the Secretary makes the determination under paragraph (1), the Secretary shall submit to the Committees on Veterans’ Affairs of the House of Representatives and the Senate an explanation of such determination. (b) Regulations (1) Proposed regulations (A) Timing If the Secretary determines under subsection (a)(1) that a presumption of service connection is warranted for an illness, the Secretary shall, not later than 180 days after making such determination— (i) issue proposed regulations setting forth the determination