I did mine on Friday, at the center in DC. The most time-consuming part of the process was finding the GE office inside the building; took less than 10 minutes to get called in once I was there, and about the same to complete the interview and fingerprinting. Flew back home today (took an extended Valentine's weekend) with Pre.

For those who may be taking the same route: get dropped off at the Reagan building, notice all the doors with signs saying you can't use them, walk around until you see the covered walkway behind the restaurant. There'll be a door in the covered walkway that you can use. Go in, get metal-detected, then head left down the long hallway to the next metal-detector station. Past that, take another left, past the reception desk, and the GE office is on the left.