Job classes

I'm trying to find out about "job classes" within an organization. I thought there are different job classes in every company, such as office personnel, scientists, laborers, etc. I thought each class can have its own set of policies re: work hours, vacation, sick time, etc.
So, my first question is: Are there such things as "job classes" in a firm?
My second question is: if there is an "office personnel" job class, can that be divided up into different segments, such as IT, Accounting, HR? If so, can each of those sub-classes have their own policies re: work hours, vacation etc? Or are there classes based upon level, such as low-level, middle management, upper management, etc, that must all be treated the same?
I'm asking because I was offered a promotion to manager with a large raise in an accounting dept. I couldn't take it because I couldn't work the hours they demanded. But, another office department, HR, does have employees (managers) who work the hours I wanted. I'm wondering if they should have allowed me, in a different department, to work the hours I requested.
Thanks so much.