Idaho Code § 42-2010
No contract shall be made by the department which requires a greater time than five (5) years for the construction of the works, but such time may be extended by the department for a period not exceeding three (3) years. All contracts shall state that the work shall begin within six (6) months from date of contract; that at least one-tenth (1/10) of the construction work shall be completed within two (2) years from the date of said contract and that the construction shall be prosecuted diligently and continuously to completion. A failure to complete the works within the time required by the contract, or an extension thereof as herein provided, shall forfeit to the state all rights under the same.
This section shall apply to contracts heretofore made as well as to contracts hereafter to be made by the department.
Idaho Code § 42-2010