In the best job I ever had in my life, my boss basically told me that she didn't care about the hours I kept or how long I worked every day as long as I got my job done. I usually showed up to work at 12pm and left around 4pm. It ended up being one of the most productive times of my life. I created products that had hundreds of millions of dollars worth of impact on the company bottom line. In my immediate next job I had to keep long hours and for some reasons I wasn't nearly half as productive.

Atleast in my life, shorter work hours tend to heavily inversely correlate with my work output.