Finished my interview yesterday.
Walked in to the DO about 15 mins before interview time, after security check reached a place where there were rooms on either side of the hall, on the right it said something like "Oath Room" so I assumed the room on the left would be the interview one, it turned out to be the waiting room, there were about 20-25 people in the room, most were for N-600? there were about 3 (including me) who had interview at the same time as mine, 10 mins past the interview time, the other two were called in, about 5-10 mins after that my number came, the Officer was very nice, introduced herself as the one who will be doing my interview. We went into her office, she asked me to remain standing up, lift my right hand and swear that I will tell the truth, she asked me to sit after that, she said we will start with the civics test, I answered the first 6 questions right and she stopped, she asked me to read "When is Columbus day" or was it "When do we celebrate Columbus day" and asked me to write "Columbus day is in October", then she started reviewing my application, on the "Do you own any taxes question" I waited for couple of seconds before answering ( I knew I had paid all my taxes not sure why I hesitated) she explained the question that she wanted to know if I had any outstanding taxes, I replied "no", I wanted to mention this since she caught my slight hesitation (lesson learnt: be confident in your answers) she then went on to review the rest of the application , at the end asked me to sign (two places) and print my name on the application, sign with the pen and not pencil on the left side of the pictures(the one I had submitted along my application), after that she stamped "Approved" on my application, she then told me she was recommending me to approval and that I should wait outside and collect my Oath letter. I waited for about 5 mins in the waiting room, got my Oath letter and left. The whole thing took less than an hour.