In addition to completion of grading, grading shall be current and shall meet the following additional time limits:

(1) Grading shall be completed not more than one hundred eighty days after the final placing of the spoil ridges. When more than one seam is to be mined, this information shall be included in the application, and the commission may defer reclamation until all seams have been mined, if such additional time does not defeat the purposes of sections 444.500 to 444.755 and there is no danger from acid mine drainage. Grading of a spoil ridge that will have an adjacent spoil ridge placed against it shall be completed one hundred eighty days after the placing of such adjacent spoil ridge. When heavy rains or other conditions make grading impracticable, the one hundred eighty day period shall be extended by the length of time such grading is impracticable.

(2) With the approval of the commission, the operator may substitute for all or any part of the affected land to be reclaimed, an equal number of acres of land previously mined and not reclaimed. If any area is so substituted the operator shall submit a map of the substituted area, and this map shall conform to all requirements with respect to other maps required by section 444.550. The operator shall be relieved of all obligations under sections 444.500 to 444.755 with respect to the land for which substitution has been permitted. However, before the commission allows such substitution, the county commission in the county affected shall determine if the substitution is in the best interest of land usage and public interest.