I shouldn't have worried as the medical was already with the Consulate despite it only taking place on the 15th (1.5 business days ago). I had my interview today and got approved! Really happy with that.
I got there around 7.20am, it was already pretty busy. Presented my appointment paper at the first kiosk and stood in line for a security check. This was slow until they opened properly at 8am, when they started taking 5 people at a time. There is a strict no laptop policy and people were turned away who had laptops and told to store them at a local store. They did emphasize that even if that made them late, they would wait for them. Mobile phones, smart watches, fit bits etc are all stored at the security kiosk. They even took my car keys and a random charging cord from my briefcase.
I went to Window 22, where they asked for a photograph (I had a couple spare US size from my last batch) and a payment. I used my Mastercard Debit. I asked if they had received my medical and the lady confirmed. She also described what would happen should the visa be approved on the day. I then waited about 15 mins to be called to another window (15 I think) where they took the rest of the required documents - birth certificate, marriage certificate, police certificates with copies and the I-864s (with joint sponsor in my case).
I then waited another 20-30 mins (no watch, no phone and couldn't see a clock) before being called for my interview at Window 19. There she went through all my documents systemically and asked me questions under oath. It took around 15-20 mins to go through everything but I felt the process was quite thorough. There were typical questions - how did we meet, where and when did we get married, who is your joint sponsor, have you served in the military and a few more besides.
Then she went through it all one more and told me that the Visa is approved, and handed me a receipt and paperwork about what to expect. I thanked her, and got myself together and back to the car. I would say all in all about 2 to 2.5 hours total from waiting in line. Pretty efficient overall.