To me the bigger size is essential, as a lot looks different, when the image is too small. Everything is more sort of concentrated/compressed and only when you view the photos full screen, everything begins to flow, the colors kind of "relax" and the eye can wander...
Skin tone is really difficult in painting too, even when you want an "artificial" look, like I often do. In oil painting I like the old masters approach to underpaint in (veronese) green, particularly in the shadows... working digital can make it a real challenge, and I can only imagine, how it can drive you nuts, with all the options.
But when you are passionate about something, there is a difference between a challenge you want to take on and a task you are supposed to accomplish. I'm sure those two hours went by like nothing and of course with the happy feeling of mastering what you wanted to do, everything else was a piece of cake!