This is brilliant, thanks for posting! Also, the best times to send an email and ensure a response is from 9pm-12am, and during the weekends. Learned that from another article.
The point that the article I read made is that it's not so much about when an email gets Opened, but when the response rate is the highest, and that occurs mainly during low traffic times, such as late at night, and on weekends. It's more about being one of a few "unread" than being available during peak traffic times.