The ephemeral property deducts maximum durability at a rate of one point per six minutes, while the item is equipped AND the wearer is actively fighting. Being in war mode does not count, nor does simply being the target of aggression. You have to actually be fighting. Also, it deducts from the 25-hour "lifetime" in 10-second increments; if you spend 10 minutes in a fight but only spend half that time in actual combat, your ephemerals will only lose 5 minutes of lifetime.
The current durability is repaired to max durability frequently. The intent is for ephemerals to last for 25 hours of actual fighting time without having to worry about keeping them repaired.
