We were the first on Thanksgiving morning to go ice skating at the outside rink at Washington Harbor.
I presume because of the holiday and early morning people were scare but that only made it better for us. The sun was shining and the view of the Potomac was amazing.
The price was $15 each adult and then another $1 for a locker for your stuff. You get a bracelet that gives you access for the day but 30-40 min was more than plenty of time.