I think this really depends on how much blood flow the ring may or may not be restricting. If there is significant restriction of blood flow, I think the 30 minute guideline makes a lot of sense. However if you are wearing something like a metal cock ring that does not restrict blood flow when you are flaccid, I don’t see any reason it can’t be worn for much longer. When all is said and done - be smart, pay attention to what your body is telling you, and be on the cautious side to prevent injury.