(a) Computation. In computing any period of time prescribed or allowed by these rules, the day of the act, event, or default from which the designated period of time begins to run shall not be included. The last day of the period so computed shall be included, unless it is a Saturday, a Sunday, or a legal holiday, in which event the period runs until the end of the next day which is not a Saturday, a Sunday, or a legal holiday. When the period of time prescribed or allowed is less than seven (7) days, intermediate Saturdays, Sundays, and legal holidays shall be excluded in the computation. As used in this rule, “legal holiday” includes New Year's Day, Washington's Birthday, Memorial Day, Independence Day, Labor Day, Columbus Day, Veterans' Day, Thanksgiving Day, Christmas Day, and any other day declared as a holiday by the President or the Congress of the United States.

(b) Additional time after service by mail. Whenever a party is required or permitted to do an act within a prescribed period after service of a document and the document is served by mail, three (3) days shall be added to the prescribed period.

(c) Extensions. For good cause shown, the Presiding Officer may extend any time limit prescribed or allowed by these rules or by order of the Commission or the Presiding Officer, except for those sections governing the filing of interlocutory appeals and appeals from Initial Decisions and those sections expressly requiring Commission action. Except as otherwise provided by law, the Commission, for good cause shown, may extend any time limit prescribed by these rules or by order of the Commission or the Presiding Officer.