At the time specified in the notice, the board shall meet and inquire into and determine the sufficiency of the petition and the validity of the signatures thereto. If the petition is found sufficient and signed by the required number the board shall make an order directing that a special election be held to submit to the electors of the county the question of the change of the county seat, and, if so, to what place it shall be moved. The board shall fix the time of holding the election, which shall be held not less than thirty nor more than ninety days after making the order. If, however, a general election is to be held in the county within six months after making the order, the board shall order that the questions be submitted at the next general election.