D.C. Mun. Regs. tit. 14, § 3816
3816.1 In computing any period of time prescribed or allowed under this chapter, the day of the act, event, or default from which the designated time period begins to run shall not be included.
3816.2 The last day of the period so computed shall be included, unless it is a Saturday, Sunday or a legal holiday, in which event the period runs until the end of the next day which is not a Saturday, Sunday or a legal holiday.
3816.3 When the time period prescribed or allowed is ten (10) days or less, intermediate Saturdays, Sundays, and legal holidays shall be excluded in the computation.
3816.4 Legal holidays shall be those provided in D.C. Official Code § 1-612.02 (2001).
3816.5 If a party is required to serve papers within a prescribed period and does so by mail, three (3) days shall be added to the prescribed period to permit reasonable time for mail delivery.
3816.6 The Commission, for good cause shown, may enlarge the time prescribed, either on motion by a party or on its own initiative; provided, that the Commission does not enlarge the time for filing a notice of appeal.
SOURCE: Notice of Final Rulemaking published at 33 DCR 1336, 1346-47 (March 7, 1986).