With the submission of its preliminary report and form of contract to the municipalities interested, the commission shall notify the municipalities of a time, which shall be not less than thirty days from the delivery of the notice at the office of the clerk of the respective municipalities, within which the municipalities shall respectively, through the board or body having charge of its water supply, submit suggested modifications to such form of contract, or signify their acceptance thereof or their intention to withdraw from further participation in the proposed development or acquisition. The commission may extend the time for municipal action, hereinbefore or hereinafter required, beyond the time fixed by it in any such notice.