D.C. Mun. Regs. tit. 24, r. 24-1318
In computing any period of time prescribed or allowed by this chapter, the day of the act, event, or default from which the designated period of time begins to run shall not be included.
The last day of a period so computed shall be included unless it is a Saturday, a Sunday, or a legal holiday.
When the period of time prescribed or allowed is less than seven (7) days, intermediate Saturdays, Sundays, and legal holidays shall be excluded from the computation.
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 shown, be extended or shortened by the Director with notice to all parties.
D.C. Mun. Regs. tit. 24, r. 24-1318