Focusing on time management leads you to do all sorts of things like calendar blocking, task batching, and to-do list triaging. You organize your life around your calendar.
A much better barometer for your day is your energy level. How are you feeling physically and emotionally right now?
Under the banner of “time management” we would be optimizing every second. In "peak" productivity where every hour is planned, there wouldn’t be time to make a salad or go for a run.
Under time management, you put in the work at the scheduled time regardless of energy level.
Under energy management, you get your energy levels right so that you can achieve the work in less time.
The good news? Unlike time, you have some control over how your energy flows.