It should give a lesser invisibility enchant with a 60 min cooldown that lasts for 15 seconds.

Really, when except for a couple times does he ever wear the ring for more than 15 seconds? He doesnt use it too often so the cooldown is fine. BUT heres the stipulation:

Undead can see through it (not horde undead as they are classified as humanoids) AND enemy player's ghosts can see and one shot you while you are using it.