What are dissertation hours in the scope of degree requirements for PhD?
In my PhD program, I was required to register for various research and dissertation related courses to fill the required 9 credit hours to be a full-time student. Those course ranged from 3 to 5 credit hours depending on what I needed. Those courses never met, and I did not receive a letter grade for them. They seemed to have two purposes: 1. existing to fill my schedule after my actual coursework was done (so that I was listed as being enrolled as a full-time student and so that they had something to charge me for), and 2. giving my advisor credit with the department for supervising a research or dissertation student. The mostly seem to be a bureaucratic slight of hand. 

Edited to add: I was also paid 20 hours per week to work as a Graduate Research Assistant, but I basically worked about 40-50 hours per week on going to class (until I was done with my required hours) and working on my research. Towards the end, when I was writing my dissertation, it was more. The hours I was officially paid and the credit hours I took, never really aligned with much, except that a 3-credit hour actual course (like "Functional Analysis") met for 3 hours every week.