Heal Stamina Plus % increases the rate at which a player character's stamina heals after running in the wilderness or sustaining stamina damage. The rate at which stamina heals while standing idle (not attacking or casting) is as follows:
Stamina healed per second = 25 * ( [Maximum Stamina * (100 + Heal Stamina) /100] /256) 
Consequently, while standing idle it takes maximum 256 frames or 10.24 (256/25) seconds to heal from zero to maximum stamina. The rate at which stamina heals while walking is as follows:
Stamina healed per second = 25 * ( [ [Maximum Stamina /2] * (100 + Heal Stamina) /100] /256) 
Consequently, while walking it takes maximum ~512 frames or 20.48 seconds to heal from zero to maximum stamina.
Player character can also heal to maximum stamina by gaining a level, entering a game, drinking a Stamina Potion, visiting a healer in town or activating a Stamina Shrine in the wilderness. Drinking from a well in the wilderness will heal 50% of maximum stamina each time.
Heal Stamina is the sum of all applicable bonuses listed below. However, this bonus is not sought since the rate of healing can also be increased by increasing Maximum Stamina, gaining levels and allocating points to Vitality (which has the added advantage of increasing the length of time players can run before they need to recover).