This subchapter shall be effective immediately for the purpose of the promulgation of charges, or the basis of computation thereof, and the execution of contracts authorized by the terms of this subchapter, but neither such charges, nor the basis of computation thereof, nor any such contract, shall be effective unless and until this subchapter shall be effective for all purposes. This subchapter shall take effect for all purposes when, but not before, the Secretary shall have found that provision has been made for the termination of the existing lease of the Hoover Power Plant and for the operation thereof as authorized by section 618h of this title, and that allottees obligated under contracts in force on July 19, 1940 to pay for at least 90 per centum of the firm energy shall have entered into contracts (1) consenting to such operation, and (2) containing such other provisions as the Secretary may deem necessary or proper for carrying out the purposes of this subchapter. For purposes of this section such 90 per centum shall be computed as of the end of the absorption periods provided for in regulations heretofore promulgated by the Secretary and in effect on July 19, 1940.

If contracts in accordance with the requirements of this section shall not have been entered into prior to June 1, 1941, this subchapter shall cease to be operative and shall be of no further force or effect.