I have BIAB installed on the boot drive of my iMac Pro except for Real Tracks and Drums installed on a SATA III SSD (USB 3 or faster doesn't make a difference—SATA III is the bottleneck). This makes a difference in the start up time since BIAB checks the status of those files on startup. As you will see, if the libraries remain on the HDD, the difference is 4 seconds.

BIAB 2020:
Build 402: start till BIAB logo disappears: 15 seconds. RealTracks & Drums installed on SSD

Build 403: start till BIAB logo disappears: 13 seconds after installation. After reboot 10 seconds. RealTracks & Drums installed on SSD
Build 403: start till BIAB logo disappears: 14 seconds. RealTracks & Drums installed on BIAB 2019 Audiophile HDD over USB 3

Just for kicks:

BIAB 2019
Build 319: start till BIAB logo disappears: 15 seconds. BIAB App, RealTracks & Drums installed on BIAB 2019 Audiophile HDD over USB 3


BIAB 2023 Audiophile, 24/60 Core M2 Mac Studio Ultra/8TB/192GB Sonoma, M1 MBAir, 2012 MBP
Digital Performer 11, LogicPro
Finale27.4, Dorico5, Encore5, SmartScorePro64, Notion6, Overture5