D.C. Mun. Regs. tit. 9, § 2005
2005.1 In computing any period of time prescribed or allowed by this chapter, the day of the act from which the designated period of time begins to run shall not be included.
2005.2 The last day of the period computed under § 2005.1 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.
2005.3 In any instance in which an act must be done within a certain number of days, the computation of time shall include only business days and, thus, shall not include Saturdays, Sundays, and legal holidays.
SOURCE: Final Rulemaking published at 45 DCR 24, 29 (January 2, 1998).