I tried 10-4 for 6 months at a company that had a mix of people working 4 and 5 days, it made me less productive and more burnt out as a senior engineer. I hav

I tried 10-4 for 6 months at a company that had a mix of people working 4 and 5 days, it made me less productive and more burnt out as a senior engineer. I have ~5 hours of productive creative energy per sleep, others may be different but that's me. Ideally I give 4 hours to the job, spend 4 hours reviewing/meeting/etc. and have 1 for myself. If I push myself beyond that, I start doing substandard work, so 10-4 meant I either did fewer hours of productive work per week, stole my personal creative hours, or delivered substandard work. I did all three depending on the week, but in any case my productivity overall suffered, that appeared in my peer reviews, and the stress slowly built up until I went back to working 5 days.