It shall be the duty of such company to complete the improvements contemplated by the plans approved as aforesaid within the time which shall be prescribed by the said board of control, at the time said plans shall be approved by said board of control, and in case of failure so to do said company shall forfeit all right to collect tolls of any person or persons whatever, who shall use for the purposes of navigation the improvements made by such company, unless the time for completing the same shall have been previously extended by said board of control, upon good cause shown and after publication of a notice of said application as required by section 5 of this act.