Nope, it is not just time spent, but what you do with that time.-
I had a friend who was a big PP follower. Spent a Lot of time with her horse. She was quite wealthy and had retired young, and would spend hours with her horse every day. A Lot of that time was spent sitting with him in the stall, 'bonding' with him on an 'emotional' level. Lots of grooming. A fair amount circling the horse with a 'carrot stick', and a very small amount of time riding, as the horse was quite unpredictable under saddle.-
At the time I was able to go to the barn 3 or 4 times a week, for about an hour or two each time. My horse was young, a bit spooky in traffic, and tended to bolt. I would tack up, and spend most of my time in the saddle.-
After about 6 months, my horse was sane in traffic, and a good all around trail horse. Her horse was much cleaner than mine, and generally quite barn sour.-
Now please let me emphasize, I am Not Joe Horsetrainer, I just like to use as much common sense as I posess. She probably spent about 3x the hours with her horse as I did with mine.-
True, I was half her age, and a confidant rider. But if she had taken 1/3 of those hours and invested in a decent trainer, her horse could have been as good as or probably better than mine. So it is more than just time, definitely.-
That being said, I did not even hear of Parelli until I had about 10 years of riding (starting at age 16) under my belt. Thought he had some fine concepts. What soured me was how intelligent people would turn into blind disciples who thought Parelli was some sort of god and that every other method was wrong. -
If you want to learn about NH, I say go ahead. But remember to keep an open mind, learn about other methods, and know that Nobody knows it all.