I researched this topic a little as it was related to work I was doing in my PhD 2-3 years ago. I'm mostly going from memory here. I think Kaufman is largely incorrect for skill learning in real-life. Walker et al. (2002) found sleep improved motor skill compared to the same amount of time spent awake, but a similar improvement was found after nightime sleep whether participants learned at 10 am or 10pm.

Walker study: https://www.sciencedirect.com/science/article/pii/S0896627302007468

Possibly, Kauffman based his claim on Robertson's studies which found interference between a motor skill task and a verbal task is minimized with sleep but Robertson doesn't directly test the claim as I think he only tests the learn in the morning group after 12 hours but not 24 hours and I tend to be skeptical even of Robertson's basic finding as when I was doing research on the topic independent researchers hadn't replicated it http://www.jneurosci.org/content/27/39/10468.short.

I also found these articles that might be of interest:

https://academic.oup.com/sleep/article/40/4/zsx036/3765296

https://onlinelibrary.wiley.com/doi/full/10.1111/tops.12232

Overall, spacing your practice will be a much more significant variable than the time of day you practice.