I remember that one of my most productive times was in ca. 1995 while building a campus-wide POS system involving a long-distance wireless network, hardware, and custom-built software that ran on low-end PCs with touch-screen displays.
I was working from Monday to Thursday starting at 9 in the morning and ending at 12 pm. The afternoons were devoted to spending time with friends, exploring ideas, and reading. We made sure that we didn’t do any work in afternoons and waited, on purpose, until the next morning. All mornings were highly productive and focused on what mattered.