Mo. Rev. Stat. § 355.391: Waiver of notice.

1. A director may at any time waive any notice required by this chapter, the articles or bylaws. Except as provided in subsection 2 of this section, the waiver must be in writing, signed by the director entitled to the notice, and filed with the minutes or the corporate records.

2. A director's attendance at or participation in a meeting waives any required notice of the meeting unless the director upon arriving at the meeting or prior to the vote on a matter not noticed in conformity with this chapter, the articles or bylaws objects to lack of notice and does not vote for or assent to the objected-to action.