Let's not confuse sports here. I don't think pool is quite as laborious as weightlifting. I don't really wanna go back and forth on this topic, I have stated my opinion and I respect others'. But I will say that if a player's max concentration time is near one hour, you have some serious work to do on lengthening that (both mentally and physically), by quite a bit too.
Also, why have we equated ability to concentrate with ability to learn/experiment and put things in muscle memory? There is some VERY poor logic out there, sorry but there is. The benefits
may not be there as much as that first hour as in say the 10th hour (I think even that is debatable), but you are still getting FAR more benefit overall with the 10 hours. The way people get better in sports is, um, practice. Once you reach a plateau, you may need to change
what you practice. The answer to this question is really simple.... who's better all things being equal.... a guy who logs in 3000 hours of practice in a year, or the guy who logs in 300? It is really an easy question, you are only rationalizing if you pick the 300.
To be honest, I think this "1 hour theory" on practice is something people tell themselves because they don't want to put in the hard work -- or can't put in the work.... or can't play well themselves for more than an hour. But don't misinform other people due to your own lack of concentration abilities or passion to improve. And I have no idea why instructors say this. Maybe to make clients feel good about playing only an hour a day (guessing).
To be a little less contentious, i'll bring up Bruce Lee. I think his philosophies for sports are superlative. He would probably say that 1 hour can work for certain people, but he'd probably add nobody should put limits like that on anything. He said you must go beyond your limits.... I don't think you can do that on an hour, but others do obviously