When you were doing this, what specifically were you doing during the 4 sets of 45 minutes? Were you attempting a certain phrase or phrases? Were you getting it right, or were there wrong notes, or something else that you wanted to improve that wasn’t improving, hence the repeition? Just trying to understand better what people are doing out there.
In general, I wouldn’t choose an arbitrary amount of time as a practice “goal”. The time isn’t really the goal anyway, it’s the end result. There are lots of unanswered questions about “practice”, in quotes, including what most people even mean when then they use the term. But in the very general sense, it sounds like you’re asking about acquiring a new skill. And really the number one obstacle there is trying to figure out how to perform the target activity correctly, recognizing the feel of doing so, and going, aha, that was it, I felt that!
If you could magically pare down your playing time to just those aha moments, then that would be the theoretically shortest amount of time you could practice. Of course, that’s not possible, so a certain amount of “practice” time, again in quotes, is spent trying to have those moments in the first place. This is where the time question arises. But again, in a very general sense, if I’m not having aha moments, there is no reason to keep playing. I’ll put it down and come back. And some days, that’s just the way it is. I’m fine with that. This is what I mean by time versus results. I want to have the aha moments, and some days you do, right away, and others you don’t. This introduces natural variability.
Keep in mind also, we’re often trying to help players who have played in some cases for decades without ever experiencing what accurate, fluid picking technique feels like. So whether they get there in five intense months or a relaxed year or year and a half is of much less consequence to me. I’m sure there is some optimal amount of aha time that will produce the most results in the shortest time, and beyond which it doesn’t make sense to keep going. But the bigger issue is that simply piling on repetition without having that feeling of “hey I almost got this” isn’t doing as much good.
So in short, you have to actually feel like you did something, it has to be recognizable as such, and generally that feeling is also easy and fast, if a little sloppy. The “long tail” of practice is cleaning things up, with gradually better accuracy over that six months to two-year window. But you should have a high bar for doing it “sort of right” immediately, with comfort and smoothness. If the hands aren’t giving it to you that day, it’s ok. They will eventually, and your job is to keep an eye out for when they do.
Re: this clip specifically, the pentatonic stuff looks like wrist with a little forearm, upstroke escape / downward pickslanting. We’re about to upload a new section to the Pickslanting Primer on precisely this subject. It is the most comfortable way I know of to play these kinds of lines, and it’s the method I’ve used in all our seminars like Cascade. The new material should be up over the next week or so.
However in the mean time I think it’s a good idea to stop playing for a while until discomfort goes away. And I’d also check in with a doctor since pain in your neck, and referred pain down your arm, sounds like nerve impingement of some kind and that’s not a good thing. It could be nothing, just temporary inflammation. But given your history with the accident it’s wise to play it safe.