I was actually going to use the Cad/ drafting process as an analogy, because in some ways it's similar.
Like you I have to track my hours at work, so I can't just play, and I am expected to produce visuals of reasonable quality.
My answer to this is to always have something on the go. So I'll do a set up before work with a focus on on issue I want to learn. Then let it render away, review at lunch, make some adjustments, and let it render again.
In this way it's not like drafting, as once your have imported the scene, worked with you materials, and lighting etc, the computer does all the work. By keeping the scenes simple, I can at least move forward in the learning process, because I know I have a long way to go.