I got there at 7am on a freezing day (with wind chill down to -20 degrees Celsius). I was the first one there. There was no formal lineup outside (so please stand close by the door if you want to get in first!). The door opened at 7:35am. Then we were seated in the basement outside the elevator after security check (again, anyone can sit anywhere regardless of when they come, so if you have your interview first, please sit close to the elevator). We were allowed to go upstairs to the 19th floor at 8am. There was a visa check in desk right in front of the elevator on the 19th to check people in. I was given "application #1" waiting ticket. A few minutes later, I was called to window 1 to submit all originals and proof of financial support. It took about 10 minutes. Then I was seated again and I was not called until around 8:45am (I was the first immigration interview of the day). The interview process took about 5 minutes. Here were the questions:
1. How long have you been married?
2. How long have you known each other?
3. What does your spouse do?
4. Where does your spouse live?
Then we chit-chatted a little bit. That was it.
I left the consulate at around 9am.
It was an ok experience as most of time was spent in waiting.
P.S. When the door opened at 7:35am, there were quite a lot of people. But most of them were for non immigration visas which had their own separate line. There were probably only 4-5 people for immigration visas. So I assume the wait would not have been long for them regardless. So arriving there at around 7:30am would have been totally sufficient.
Update: Visa was indicated as "issued" on Wednesday and the Consulate decided to mail it out on Friday. Of course, Loomis is closed on the weekend. Now I have to rebook my plane ticket. Bad experience all the way from USCIS through passport delivery.