D.C. Mun. Regs. tit. 14, r. 14-3816
Where this chapter or any order of the Commission specifies a time period, any reference to "days" shall mean all calendar days, unless specifically designated as "business days."
"Business days," where expressly used in this chapter or by order of the Commission, shall be all days other than Saturdays, Sundays, legal holidays codified at D.C. Official Code § 1-612.02, furlough days, and other closed days as designated by the District of Columbia Government.
In calculating any time period specified by this chapter or by order of the Commission, the day of the act, event, or default from which the time period begins to run shall not be included.
In calculating any time period specified by this chapter or by order of the Commission, the last day of the period shall be included, unless it is not a business day, in which case the period shall end on the next business day.
In accordance with § 3803.5, a party's obligation to serve any pleading, motion, or other document on another person, if done by U.S. mail, shall be deemed complete on the date of mailing.
If a party is permitted or required to act within a specified time period after an event, such as the issuance of any order or the service of a motion by another party, if the party has been served with the order, pleading, motion, or other document by U.S. mail, five (5) days shall be added to the time period for the party to act.
In accordance with § 3801.2, a party's obligation to file any pleading, motion, or other document with the Commission shall be deemed complete only upon actual receipt by the Commission during its regular business hours, regardless of how the filing is made.
The Commission may enlarge the time period specified, either on motion by a party or on its own initiative in accordance with § 3815; provided, that the Commission shall not enlarge the time for filing a notice of appeal except as provided by § 3815.3.
D.C. Mun. Regs. tit. 14, r. 14-3816