“You are most productive in the morning.” — That is a bold assertion of fact that is too great a generalization to be an actual fact. Some people are most productive in the morning, not all people.
I, for example, am lousy in the morning. I am not a morning person … and I hate people who are and assume everyone else is. But come mid-afternoon, I am on fire and my productivity soars and I can easily work and work and work well into the night. Indeed, when I’m on a roll, I could work all night (greatest job I had was in grad school when I worked third shift, midnight to eight!).
So please, don’t write things suggesting that it is a scientific fact that people — all people — are most productive in the morning and are at peak performance for only 90 minutes. That might be true for some people, but it is likely untrue for many, many people.
Also, as somebody else pointed out, the “advice” from this little article is largely useless because it is divorced from reality — most people do not have the kind of control over their morning schedule to implement this half-baked advice.