context: The film begins with a totally white screen and as the sun sets, the image of the Empire State Building emerges. The floodlights on its exterior come on, the building's lights flicker on and off for the next 6Â½ hours, then the floodlights go off again in the next to the last reel so that the remainder of the film takes place in nearly total darkness.[2]
  The film was shot with Warhol directing and filmmaker Jonas Mekas working as cinematographer. During three of the reel changes, filming recommenced before the lights in the filming room were switched off, making the faces of Warhol and Mekas momentarily visible in the reflection of the window each time.[3]
question: For Empire how long did Andy Warhol shot?
answer: 612 Hours