Nice Article. Its kinda the Stuff i read time and time again when it comes to practicing.
I think the most helpful thing in practicing is analysing what exactly went wrong. Because if you dont know the Problem its hard to actually fix the Problem.
I personally wouldnt even have the time to invest 6 Hours a day in Playing the instrument. I Usually aim for about 30 minutes. But it usually becomes a bit more because its mixed up with just playing for the fun of playing.