D.C. Mun. Regs. tit. 23, r. 23-1702
Whenever a party to a proceeding under this chapter has the right or is required to perform some act within a specified time period after the service of notice upon the party, and the notice is served upon that party by mail, three (3) days shall be added to the prescribed period.
Except as otherwise provided by law, any time period prescribed by this chapter may, for good cause shown, be extended by the Board with notice to all parties.
For purposes of computing time that is stated in days or a longer unit of time, exclude the day of the event that triggers the computation of time.
For purposes of computing time that is stated in days or a longer unit of time, every day, including intermediate Saturdays, Sundays and legal holidays is counted. Count the last day of the period, but if the last day is a Saturday, Sunday or legal holiday, the period continues to run until the end of the next day that is not a Saturday, Sunday or legal holiday.
For purposes of computing time that is stated in hours, begin counting every hour immediately at the conclusion of the event that triggers the period, including hours during intermediate Saturdays, Sundays and legal holidays. If the time period would end on a Saturday, Sunday, or legal holiday, the time period continues to run until the same time on the next day that is not a Saturday, Sunday, or legal holiday.
Unless a different time is set by a statute, regulation or Board Order, the last day of a specified time period is at midnight for electronic filing, and at the close of business on the last day for filing by any other means.
D.C. Mun. Regs. tit. 23, r. 23-1702