This is my opinion from personal experience, i don't know how your body handles chemicals but.
I don't think 20mgs oxymorphone
would cause an overdose, especially taken orally with the time release intact, combined with your tolerance to opiates
in general. The most i have done is 30mgs with no tolerance at the time and this was the old ones so they could be snorted to release it all instantly. Kept nodding off every 5 minutes then waking up with lotsa energy but i was far from feeling 'bad' in any way. It was the most fucked up i have ever been by all means, no other opiate
experience came close to that.
Can't comment on the time release frame as i have never and would never take an opana orally, they are worth way too much coinage for that.
Take my advice with a grain of salt though.