Speedpaint practice, I suppose. I'd approached four hours, and figured that's a good place to stop.
Normally I like to do multiple PS layers like:
highlight [clipping mask]
shadow [clipping mask]
color Fill [clipping mask]
figure's fill region
But this time I just kept on creating new line layers over coloring layers over line layers over... etc. while merging the layers below as I went. I think I really just put this thing together with one layer essentially.
I guess that's faster.