For morning people, meaning the 10%-20% of humans with the lark chronotype, this is true, but these are the only people who are productive from 6am-8am.

Some bears (60% of people) are also too tired and low-focus by the evening, so this advice can work for them to work from 8-9am.

Wolves (10%) like myself, also known as night people or night owls, definitely reverse this statement: every hour after 5pm is worth 2 hours before 9am.

Dolphins (10-20%) are always tired.