Cortisol levels decrease 20- to 30-fold from morning to night in a healthy individual.
"Like cortisol goes up, cortisol goes down. It drops 20-, 30-fold from the morning until night in a healthy individual." (said at 1:50:08)
No published studies retrieved in this search established a 20- to 30-fold decrease in cortisol levels from morning peak to nocturnal nadir in healthy individuals. While human cortisol follows a robust diurnal circadian rhythm peaking shortly after awakening and reaching a nadir around midnight, literature typically reports a substantially smaller diurnal fold decrease (typically on the order of 3- to 10-fold in serum/plasma or saliva), making the 20- to 30-fold figure unverified in the retrieved records.