(a) In computing any period of time prescribed or allowed by this Court Operating Rule 12, the day of the act, event, or default after which the designated period of time begins to run is not to be included. The last day of the period so computed is to be included, unless it is a Saturday, Sunday, or a legal holiday in Missouri, in which event the period runs until the end of the next day which is neither a Saturday, Sunday, nor a holiday.

(b) When by this Court Operating Rule 12 or by statutes an act is required or allowed to be done at or within a specified time, the commission for cause shown may at any time at its discretion:

(1) With or without motion or notice order the period enlarged if request is made before the expiration of the period originally prescribed or as extended by a previous order, or 

(2) On notice and motion made after the expiration of the specified period permit the act to be done where the failure to act was the result of excusable neglect. In no event, however, may the commission extend the time period prescribed in Court Operating Rule 12-23.01.