Mo. Rev. Stat. § 138.090: Meetings of board (first class counties).

1. Except as provided in subsection 2 of this section, the county board of equalization in first class counties shall meet on the third Monday in July of each year.

2. Upon a finding by the board that it is necessary in order to fairly hear all cases arising from a general reassessment, the board may begin meeting after July first in any applicable year to timely consider any appeal or complaint resulting from an evaluation made during a general reassessment of all taxable real property and possessory interests in the county. There shall be no presumption that the assessor's valuation is correct.