(a) Computation. In computing any period of time prescribed or allowed by the rules in this part, 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 7 days, intermediate Saturdays, Sundays, and legal holidays shall be excluded in the computation. As used in this part, “legal holiday” includes New Year's Day, Washington's Birthday, Memorial Day, Independence Day, Labor Day, Columbus Day, Veteran's Day, Thanksgiving Day, Christmas Day, and any other day appointed 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 under this part or by order of the Administrator or the Presiding Officer, except those governing the filing of interlocutory appeals and appeals from Initial Decisions and those expressly requiring the Administrator's action. Except as otherwise provided by law, the Administrator, for good cause shown, may extend any time limit prescribed under this part, or by order of the Administrator or the Presiding Officer. A party or participant may petition the Presiding Officer or the Administrator, as appropriate, for an extension under this paragraph. Such a petition shall be filed prior to the occurrence of the time limit which is the subject of the petition.