D.C. Mun. Regs. tit. 3, § 401
401.1 In computing any period of time prescribed or allowed by these rules or by any applicable statute, the day of the act, event, or default from which the designated period of time begins to run shall not be included.
401.2 The last day of the computed period shall be included unless it is a Saturday, Sunday, or legal holiday, in which event the period shall run until the end of the next day which is not a Saturday, Sunday, or legal holiday.
401.3 When the period of time prescribed or allowed is less than seven (7) days, intermediate Saturdays, Sundays, and legal holidays shall be excluded from the computation unless an applicable statute expressly provides otherwise.
401.4 Subsection 401.3 of this section does not apply to proceedings pursuant to D.C. Official Code § 1-1001.08(o) (2006 Repl.).
401.5 For the purposes of this chapter, "legal holiday" includes the following:
(n) Any other day designated a holiday by the President of the United States or the District of Columbia government.
401.6 [RESERVED]
401.7 When an act is required or allowed to be done at or within a specified time, the Board for cause shown may at any time in its discretion, do either of the following:
(a) With or without motion or notice, order the period enlarged, if a request for enlargement of time is made before the expiration of the period originally prescribed or as extended by a previous order; or
(b) Upon motion made after the expiration of the specified period, permit the act to be done where the failure to act was the result of excusable neglect.
SOURCE: Final Rulemaking published at 45 DCR 432 (January 23, 1998); as amended by Final Rulemaking published at 70 DCR 015793 (December 15, 2023).