The Circle of the Shepherd druid's Spirit Totem feature lets the druid summon a spirit that creates an aura with a certain effect. One option for the type of spirit is the Bear Spirit (XGtE, p. 23):
Bear Spirit. The bear spirit grants you and your allies its might and endurance. Each creature of your choice in the aura when the spirit appears gains temporary hit points equal to 5 + your druid level. In addition, you and your allies gain advantage on Strength checks and Strength saving throws while in the aura.
The PHB ruling says that unless otherwise stated, temporary HP can last until the character that receives it takes a long rest. Now, I am planning to use the Bear Spirit before short or long rests to provide my team some temporary HP. My fear is that it might be too OP.
How long does the temporary HP from the Shepherd druid's Bear Spirit Totem last?