Arrived at 11.15am for my 12pm appointment, and went in straight away, was waiting for about 45 mins until I handed in my documentation to a very nice British gentleman. Waited another 45 minutes or so and was called to another window. Spoke to a really nice American gentleman who asked, how did you meet etc.
As many other reviews, just be yourself, I did honestly feel like I was just talking to an acquaintance or a friend about my fiance as I have 100s of times and I'm sure you have, took about 5 minutes and then approved!