There should be a timer on the ring counting down. When that timer hits 0:15, you will be able to use the ring again (aka 16 hours after you last used it)
The part that has 0:00 in this pic should be a timer on yours yes? When the timer in that spot hits 0:15 (the charge time after you equip the ring before you can use it), you can use your exp band again.
Also most Enhancing effects are lost if you take off the equipment, including the Hydra gear from Dynamis-Tavnazia.