http://www.flyreagan.com/dca/dca-nighttime-noise-ruleDue to advancements in aviation technology, the majority of the aircraft currently operating at Reagan National between 10 p.m. and 6:59 a.m. comply with the DCA Nighttime Noise Rule.
However, the Airports Authority still audits, investigates and enforces the Nighttime Noise Rule to ensure aircraft are in compliance. Non-compliant aircraft may be fined up to $5,000 per violation by the Airports Authority.
It is not called a curfew but the effect is similar. Certain airplanes, sometimes only when above certain weights, will be fined for operating outside the stated hours.
Operationally it is treated the same as a curfew. Many will use the term "curfew" to describe the situation. I'm not sure I see the importance of correcting them.