Time can never be destroyed. I have a theory that Ozpin’s semblance revolves around his lifetime. If he gets killed, he can rewind his time and restore the year before his “death”. Sounds OP, right? Well, here’s the catch. If he dies at 50 years old, he wont be able to rewind the time after he was 50. And when he gets old and reach 50 yrs old, he dies and rewinds that same year(if hes not killed, he’ll stay 50 forever). The only way to kill him is to continuously destroy him until ozpin rewinds back to his time of birth.