Chapters Have Been Uploaded! (Patreon)

The app determines how much sleep you need based on your activity level throughout the day (it records all heart rate data for 24 hours), which is calculated via heart rate patterns. The minimum amount of sleep I need based on day to day activity fluctuates between 6 hours and 50 mins to 7 hours and 40 mins. For peak performance, it's always 9 hours or more for me.  

The name of the app is "WHOOP"