12 years of logging data and the answer is give or take what you said. Every hour past 7pm is exponentially worse productivity wise (aka 7 to 8 vs 9 to 10 vs 12 to 1 is night and day). There’s also a catch up factor above which subsequent periods are impaired.

Basically if @20/30 hours per week it’s 70% ish productive at 60+ it’s max 50% which tells you a ton about the marginal productivity of those incremental hours.

There’s also time of week variation, time of day variation, the aforementioned burnout recovery spillover occasionally and a bit of sequencing at play.