D.C. Code § 6-904
No person having authority to prevent shall permit any building or part of building condemned to be occupied, except as specially authorized by the Board for the Condemnation of Insanitary Buildings under the authority contained in this chapter, after 15 days, exclusive of Sundays and legal holidays, or within such additional time as may be fixed by the Board, from and after the date of service of a copy of the order of condemnation on the owner of such building; or, if a copy of such order of condemnation has been affixed to the condemned building or part of building at a date subsequent to the date of service of the notice on the owner, after 15 days, exclusive of Sundays and legal holidays, or within such additional time as may be fixed by the Board, from the date on which said copy of such order of condemnation was so affixed.
D.C. Code § 6-904