I agree it isn't really clear what they intend to mean.
But if you consider that you will need to be a Jman at least two years and that there are 730 days in two years, that means if you must get 12000 hours in those two years that is over 16 hours a day and doesn't even allow for getting any days off at all.
You do not have to get 12000 hours in two years, obviously 6 years work.
I remember when I was getting my wastewater licenses, there is a class 4, a class 3, a Class 2, in a Class 1, the last of which is an unlimited license to run any plant in the state of Virginia. You can skip the class 4 exam and go straight to the class 3, however sitting for that requires 4000 hours on the job, 2 years of schooling, or an acceptable combination of the two. I had the combination of the two, Sat for the exam and passed it with neither 4000 hours of training nor 2 years of school.
After that you have to wait a year before sitting for your class 2 exam, and another year for sitting for your class 1. The reality is you cannot accrue hours any faster than this because you can only take school so fast, and even working a ton of overtime barely makes a dent into 2000 hours
The position I worked technically required you to obtain a class 1 license within 8 years of obtaining the position, though I know guys way past that without their class 1 licenses.
Those licenses really only mattered as far as pay went and promotions. Sure the education is important, however law only requires that a licensed operator, 1 person, be available at the plant. There were times at one plant I worked at when neither operator on shift not only lack the license, neither operator had been there more than a month.
Quite a bit different in the electrical world. Having your hours documented from a license master electrician is the most important thing