Minn. Stat. § 216I.20: IMPROVEMENT OF SITES AND ROUTES.

A permittee that acquires a site or route in accordance with this chapter may proceed to construct or improve the site or route for the intended purposes at any time, subject to section 216I.18, subdivision 2, provided that if the construction and improvement has not commenced within four years after a permit for the site or route has been issued, the permittee must certify to the commission that the site or route continues to meet the conditions upon which the site or route permit was issued.