[evrimfeyyaz]

This is close to my experience as well. If I want to do anything else that day, such as cook, exercise, relax for an hour, maybe practice the guitar, the maximum I can do is around five hours. For anything above that, I have to be super strict and/or give up other activities.

[chrisbennet]

I used to get most of work done in the morning when I had the most mental energy. If I could, I would avoid interruptions - answer emails after lunch, etc.