HRV and Cortisol Cycle

Anyone know about using HRV measurements to get an idea of their cortisol cycle?

Your cortisol levels are supposed to rise in the morning and fall in the evening.

There was an episode of the Ben Greenfield Podcast where Dr. Craig Koniver talked about tracking your cortisol by tracking your HRV.

There seems to be pretty good correlation between heart rate variability and cortisol, but you don’t want data all the time. So, the point there is you want to collect morning heart rate variability and nighttime before you go to bed.

From: [Transcript] – Cortisol Decoded: The Myths & Truths About A Hormone Crucial To Your Health & Survival

Link to Podcast

But I couldn’t find any specifics on how to do this.

I have an Oura ring. Do I just take an HRV reading in the morning and look for it to be at its lowest (more stressed state, higher cortisol). And take one at evening and look for it to be at its highest? How should these readings compare to the night time readings that Oura gives?