Here is a really interesting (and short!) video from Dr. McGuff in 2018 answering the question: "What is the best routine, and what is the best frequency?"
His answer was a little bit surprising. Essentially, he says it’s fine to start out with 3 times a week to begin, and as progress slows down, back that off to 2 times a week, and when progress again begins to slow at two days a week, drop down to 1 day per week. Basically, his point is to do BBS workouts as fast as you can recover…
I’ve been easing back into BBS after 7 months off, and it probably would have been smart for me to have done it this way to scale back up to full weight quickly. When I was doing 550lbs on the leg press, that was about a week, but it’s unlikely I was maxing out my recover potential when I started back up at 270lbs. I’m doing them differently than I used to, by going well past 90 degrees (in CrossFit parlance “ass to grass”), so they are much more challenging, but I probably left a lot of rapid progress on the table. I’m not worried about it though: progress not perfection!
This may be of interest to you @Meerkatsandy, since you’ll just be starting out with BBS in a few weeks, will be starting with low weights to be conservative, but have a bit of experience with resistance training.