Just did mine in 10th May.
We arrived at 11:20ish for an 11:50 appointment. The building is undergoing some work so it's a bit helter-skelter there. First thing you do is show your appointment confirmation to the person at the door who will send you to security.
Security took a minute, if that. Bags and coats on the belt, no metal in your pockets. Easier than the airport.
Then you go up a few floors until you find the level for in-person appointments. Go to reception. You can check in 15 minutes before your scheduled appointment. We arrived 20 minutes early and they had us wait. At the desk, present the passports, appointment check list (from email) and the FLR form with signed declarations at end. They will check you in, return your documents, give you a number, then send you to the side to wait for your number to be called.
When your number is called, you will be directed to a desk in the first part of the room. The person will ask for passports and the application form. They will also give you a folder into which you place all your supporting documents. My lady said take everything out of sleeves and separators except for the photocopies. The person enters your basic info and makes sure the form is all set. This took about 20 minutes. Then, you take your documents in their new folder and wait to be called for biometrics.
Biometrics is down a further hallway. You will be called to a booth with a desk, a stool, and a camera on the way. Give your application to the person at the desk (make sure everything is in it because this is when it gets sent for processing). They will take your fingerprints and your photo. At this point, you are done with the appointment bits; now comes the wait.
If you leave the appointment area, down the hallway is a huge waiting area. There are some tables but mostly chairs. There is a tiny café bit. This is where you wait for the decision. There are screens on the wall that show you where your application is at: awaiting arrival, biometrics verification, awaiting review, under consideration, decision made. You can watch your number go through the stages which is rather nice. If there is an issue with something, they will call you back to a desk (people in front of me had an issue with biometrics). When a decision had been made, your number is called to a desk in the first room where your documents are returned and you are informed of the decision.
All in all, it was a fairly easy experience. Just be prepared for a lengthy wait. We spent 4 hours in the waiting area. Definitely bring a book or something. There was no WiFi. Also consider bringing snacks because the café doesn't have a ton of choices. But the same-day response is so worth sitting there for a few hours.
Let me know if you have any more questions or anything. Hope your appointment goes as smoothly as mine.