D.C. Mun. Regs. tit. 10, r. 10-B2012
In computing any period of time specified in §§ 2010 through 2027, calendar days shall be counted.
In computing any period of time specified, the day of the act, event, or default after which the designated period of time begins to run shall not be included.
The last day of the period computed under this section 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 holiday.
When the period of time is five (5) days or less, intermediate Saturdays, Sundays, and holidays shall not be counted.
Whenever a person has the right to or is required to take some action within a prescribed period after the service of a notice or other paper upon him or her and the notice or paper is served by mail, two (2) days shall be added to the prescribed period.
Except as otherwise provided by law, whenever an act is required or allowed to be done at or within a specified time, the time fixed or the period of time prescribed may for good cause be extended or shortened by the Board.
D.C. Mun. Regs. tit. 10, r. 10-B2012