IQ store link: https://apps.garmin.com/en-US/apps/123d4599-7532-4cae-a706-2f0222201661
My data field shows histogram of time spent in each heart rate zone.
Like for Heart Rate Circles, zones are calculated relative to max heart rate from user age, 208 - 0.7 x age (this formula told to be more accurate than 220-age).
For zone boundaries, Garmin defaults are used: 60%, 76%, 88%, 96% respectively.
Hope it will be useful for someone!