Mine was 30 mins max. Don't know what it's like elsewhere. They gave a little speech (I heard it twice within two weeks and both times exactly the same). Played a video, we stood and repeated the oath, they played another video (America the Beautiful), I think he said something else and that was it I think.
They took our green cards on the way in and on the way out we were give our naturalization cert. At my location there were people downstairs to help you register to vote.