D.C. Mun. Regs. tit. 11, r. 11-3001
In computing any period of time specified in this title, calendar days shall be counted.
In computing any period of time specified in this title, the day of the act, event, or default after which the designated period of time begins to run shall not be included.
The last day of the period computed as provided in § 3001.2 shall be included unless it is a Saturday, Sunday, or official District of Columbia holiday, in which event the period shall run until the end of the next day that is neither a Saturday, Sunday, nor holiday.
Whenever a party has the right or is required to do some act within a prescribed period after the service of a notice or other paper upon that party, and the notice or paper is served upon that party by mail, three (3) days shall be added to the prescribed period.
Except as otherwise provided by law, whenever an act is required or allowed to be done at or within a specified time, the Commission may, for good cause, extend or reduce the time fixed or the period of time prescribed.
D.C. Mun. Regs. tit. 11, r. 11-3001