Randy,
I knew you and Scott teach that you should play in about 15-20 minute increments because of what you guys perceive to be the concentration factor. Correct?
However, if I practiced for 6-8 hours in two sessions of 3-4 hours, i'd have no problem keeping my concentration.
r/Mike
Every human is a little different.
I say keep it up. After a year if that doesn't work, try something else.
randyg