After the Secretary approves a State plan submitted under subsection (b) of this section, he may, but shall not be required to, exercise his authority under sections
of this title with respect to comparable standards promulgated under section
of this title, for the period specified in the next sentence. The Secretary may exercise the authority referred to above until he determines, on the basis of actual operations under the State plan, that the criteria set forth in subsection (c) of this section are being applied, but he shall not make such determination for at least three years after the plan’s approval under subsection (c) of this section. Upon making the determination referred to in the preceding sentence, the provisions of sections
(except for the purpose of carrying out subsection (f) of this section), 658, 659, 662, and 666 of this title, and standards promulgated under section
of this title, shall not apply with respect to any occupational safety or health issues covered under the plan, but the Secretary may retain jurisdiction under the above provisions in any proceeding commenced under section
of this title before the date of determination.