D.C. Mun. Regs. tit. 15, r. 15-117
When the time prescribed by Chapter 1 or 2 of this title for doing an act expires on a Saturday, Sunday, or legal holiday, that time shall extend to and include the next succeeding day which is not a Saturday, Sunday, or legal holiday. The computation of that time shall exclude the day of service or notice.
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 pleading upon that party and the notice or pleading is served upon that party by mail, three (3) days shall be added to the prescribed period.
Each party is bound by the type of service it receives, regardless of how other parties are served. This subsection shall not apply to filings required by the Commission.
Except in the case of jurisdictional time periods prescribed by statute, when an act is required or allowed to be done at or within a specific time, the Commission on its own motion for good cause shown may order the period enlarged.
The Commission may order an enlargement of time with or without motion or notice if request therefore is made before the expiration of the period prescribed, or upon motion made after the expiration of the prescribed period.
Unless otherwise specified, when a party has the right or is required to do some act within seven (7) days or less under this chapter or pursuant to a Commission order, Saturdays, Sundays and Commission holidays shall not be counted.
Unless otherwise specified, when a party has the right or is required to do some act in greater than seven (7) days under this chapter or pursuant to a Commission order, Saturdays, Sundays and holidays shall be counted.
D.C. Mun. Regs. tit. 15, r. 15-117