CVS MinuteClinic is a retail clinic inside of CVS Pharmacy in Washington but unfortunately we don't currently know the hours in which the clinic is open. They are located at 6 Dupont Cir NW. Of course it's always best to call in advance to confirm hours of operation before walking in.
Retail clinics offer a wide range of services overlapping considerably with those of a traditional walk-in urgent care center. That said, they are usually staffed by a Practitioner (NP) rather than a medical doctor and generally do not have an on-site x-ray or lab services, which will prevent them from seeing patients with more advanced injuries and illnesses.