I recall, while I was still taking courses in grad school, it was like 2-3 hours in class/day, and maybe 2-3 hours in the coffeeshop or lab working on research, plus teaching/grading work. When I was done with courses, it was a little less intense, but still at least 3-4h/day
Now, to the extent I can even call myself an independent researcher with a straight face, I spend maybe 4-5 hours a week... like one afternoon. Something like 10-20% of grad school level. And that's on a good week. I see no line of sight to getting up to 20-30 hours.
I think all the talk of indie research/scholarship etc. are basically impossible if you're also earning a living doing something else. Ie you have to be retired-early and independently wealthy.
Only reason I’m able to do independent research is because, in addition to a separate long term consulting engagement, it pays enough to mean I don’t need more clients now. I could maybe fit one more in, but I don’t feel any pressure to go looking. It’s stable-ish work.