vince,
if you re practicing, then you need a goal. Further stuctured practice is also important as RandyG has shown up nicley (how you see from the example how he trains).
When you start to practice concentrated on drills, patterns or stroke (or combined) you ll see soon how hard that can be

Worked last friday with a student who never practiced concentrated for 2 hours a special drill. He oftenplays 9-ball or 8-ball for hours..no problem for him, but luckily he felt, that this will not improve his game.
After these 2 hours he looked like he has done a 2 hours training in the gym...lol- he said that he never felt that much tired before

2 hours with 1 or maybe 2 drills with an exact goal/target 3 times a week is a good advice from my side- working on your fundamentals (stroke, alignment, minimizing body-movement etc). How long and how often you work on your fundamentals like stroke, alignement etc depends also on your already earned abilities. As time goes by you ll see, that the *art of training* will change.
You could download hundreds if not thousand of drills-- but it have to make sense for you my friend. Perhaps it would be good, if you would visit a good instructor who could teach you some stuff about fundamentals and how to work on yourself on them- and furthermore he will show you also, how you can create a structured practice program for yourself to reach your specified goal (you always need a goal for practice!!).
You re lucky to have many good instructors in the states. It would be an investment for a lifetime. And about your inpatience...this just shows, that you re on fire and have the willing to want more. -you ll will learn to be more patient, don t worry
lg from overseas,
ingo