Assuming you want to keep working ~40 hours a week, I feel like the best idea are four 8.5 hour days and Friday as a half day. This gives you half a day to "decompress" and still have a two day weekend ahead of you. This is the working time model most common in my country.

In the late 90's I worked at a company that had 36 hours a week. If you came in regular times, you'd get Friday afternoon off. I used to come in a bit early and leave a bit late on Monday to Thursday and then take the entire Friday off.