D.C. Mun. Regs. tit. 9, § 2023
2023.1 When the last day prescribed by these rules for performing any act falls on a Saturday, Sunday, or legal holiday, the performance of the act shall be considered timely if it is performed on the next succeeding day which is not a Saturday, Sunday, or legal holiday.
2023.2 The term “legal holiday” means a legal holiday in the District of Columbia.
SOURCE: Final Rulemaking published at 60 DCR 9888 (July 5, 2013).