Well, heres my take.
Long term is where you start seeing the average conistent results you have been aiming for over at least 6 months. Ok, thats not long term, thats what you should be doing.
I really don't think you can say you have begun the long term unti lyou have found your game. I have been playing for about 2 years, seriously for about 18 months, and have just in the last 6 months felt my game has a reached a consistent playing level that I could be happy with. Of course I'm constanly trying to improve, but I have reached a level where the level of improvement will not be exponentional any more. I think the long term cannot begin until you have reached such a point where your game will not change significantly anymore.
That being said, mathmatically, I have no idea what the true long term is. I think you must really ignore the 'long term' and focus on the here and now. We do this by playing for the long term

. We make the right plays with right percentages now, and let god sort'em out later. Meaning we earn our sklansky chips now, and someday, it will pay off.
I truly believe some players can never hit the 'long run'. MAybe they're just cursed, but its statistically POSSIBLE to never hit a flush draw (VERY unlikely, but POSSIBLE). I dunno, I don't really believe in Karma, but I sure aint voting against it. Whats the long run for these types of people? 10 years, 25? 100? 1 million? Sure love to ride that upswing though.