D.C. Code § 32-1051.02: Minimum work week.

The minimum work week for a building services employee shall be 30 hours; except, that when a covered employee is taking covered leave, the leave shall count towards the 30-hour minimum work week; provided, that at each covered location up to 20% of the work hours scheduled for covered employees engaged in cleaning service may be preserved for part-time covered employees with a minimum shift of 4 hours per night and 20 hours per week per covered employee for up to a total of 10 part-time positions permitted per covered location.