Given that enchanted items may have several uses "per day", an obligatory question is: When does a "hermetic day" begin? Sunrise? Midnight? Or do individual uses take 24 hours to "recharge"?
It's not explicitly stated anywhere that I'm aware of. Personally, I let the the enchanter decide during item creation.
That or default to sunrise. And if no sunrise exists, when the sun is at it´s zenith, regardless if it´s over the horizon or not.