What is biological prime time productivity?

Example: You have a complex financial model to build and forty emails to answer. Your energy log from the past two weeks shows your cognitive peak runs from 9:00 to 11:30 AM and your trough hits between 1:30 and 3:00 PM. Last Monday you answered email during your peak and attempted the model at 2:00 PM — it took four hours and contained two errors your manager caught. This Monday you flipped the sequence: model from 9:00 to 11:00, email batch from 1:30 to 2:30. The model took ninety minutes, error-free. The emails took the same forty-five minutes they always take — because email does not care when you do it. Same tasks, same person, same day. Different sequence. Radically different output.

This concept is part of Time Systems in the How to Think curriculum.