Hello all! I finally received my biometrics letter (hooray!) and went and did my actual biometrics this past Saturday at my local post office branch.
For timing, I received my biometrics invitation letter about exactly 1 month after receipt of my application was confirmed in Durham.
Just for my own peace of mind, I wanted to double check that I do not need to mail anything in for my biometrics. The post office stapled receipts to the letter I brought with me, and I'm assuming I keep those, along with my letter they sent me confirming receipt of my application.