I am so relieved, my BRP just came in the mail today!
Here's the timeline I had (I switched from a tier 4):
Application submitted: 9 Jan 2018 (by post)
Payment taken: 12 Jan
Letter of acknowledgement: 16 Jan (dated 11 Jan)
Biometrics invite letter received: 22 Jan
Biometrics submitted: 22 Jan
Request for more docs: None
BRP received: 22 Feb
Decision letter/original docs returned: Probably in the next few days
I guess this is actually a 2018 timeline, but hey, I'm excited and everyone here was so helpful and I figured I'd leave this timeline here for anyone else who's anxiously awaiting their decision. Thanks everyone!