I did this tour in June of 2014. It's very easy.
You line up on the street at a holding area, and your group is ushered up at the approved tour time. Security is tight - bring nothing - no backpacks, no purses, nothing. After screening, you're shown through another crowd control door or two, until you finally end up in a room at a corner of the building. You walk along the route, where docents explain the purpose of various rooms, until you end up heading out the front door. You never get off the floor you enter on, and there are maybe a dozen rooms and hall areas you walk through. The tour took maybe 30 minutes.
It was actually quite interesting, to know you're standing in the East Room, or whatever, where this or that historical event took place. I found the artwork most interesting. Portraits and such I've seen only in books are right there on the walls. Kind of cool.
Dave