The provisions of section
207 of this title shall not apply with respect to employees for whom the Secretary of Labor is authorized to establish minimum wage rates as provided in section
206
(a)(3) of this title, except with respect to employees for whom such rates are in effect; and with respect to such employees the Secretary may make rules and regulations providing reasonable limitations and allowing reasonable variations, tolerances, and exemptions to and from any or all of the provisions of section
207 of this title if he shall find, after a public hearing on the matter, and taking into account the factors set forth in section
206
(a)(3) of this title, that economic conditions warrant such action.