I've tried reducing hours (as a freelance remote developer). I cut my working hours to 25 per week from somewhere around 60ish per week. (And I could afford losing out money)
At first, I felt I was missing something. I thought it was the money. After being completely off work for a month, I realized I was missing the people (Slack chats, meetings, fire-fights)
When I started back with another client, working just 25 hours per week was much much much harder. None of these worked: 8x3days, 4x6days, 6x4days, 5x5days. Few weeks I could not even complete 15 hours, and other weeks I was over-working. I was still stressed. Finally, what worked was odd - (10-12 hours)x2.5 days. So I ended up working a bit more hours than I wanted to. It was proven again that it takes time and focus to pickup momentum and costs a lot more to loose it frequently. And I still work on my other stuff totalling to about 45-50 hour work-weeks and still feels much less stressful.