I hear you. I actually do my best work in the evenings, but the same principle applies. I would love to go part-time, and my job does actually offer that on a case-by-case determination. I may explore it a little down the road. People like @jakeybrown who just told me that he went to 30 hrs, M-W, encourage me to find solutions that don't involve just quitting outright. Haha.

But like you say, it is more than just time. It really is mental and emotional space and energy. You cannot perform for all of your waking hours. There has to be rest.