Hemingway tried not to write for any more than six hours per day. After that, he became tired and the quality dropped. If he stopped while things were still going well he avoided the risk of becoming stuck. By setting aside his work until the next day, Hemingway could allow his subconscious mind to continue working without his brain becoming tired.
There’s a ton of wisdom packed into this quote. One, don’t overwork yourself—you’ll just get exhausted and your output quality will drop. Two, stop on a high note. It’s easier to come back to your project when you have something to look forward to instead of a big problem. Three, when you’re not consciously working on a project, it doesn’t mean your brain isn’t. Inspiration can come anywhere, anytime—despite your preferred work schedule. Keeping all of this in mind, it’s easier to enjoy your time off and get more done when you are working.