I would not do this without Global Entry and airline status.

- Between summer peak travel season and the sequester you could easily have significant delays at customs. You also have to factor in the annoying moon buggy ride to the international arrivals area and any delays at baggage claim. I would not plan on being out of the airport before 1:30 even with GE. Figure 2pm without GE and it could easily be longer.

- I-66 is often congested on Saturday afternoons in summer, especially if it's a nice day or there is any type of event happening in DC. So you could easily end up at DCA with less than an hour to spare. And..

- TSA lines can be problematic at DCA - status will help you here.