Opanas are my favorite so I have done this a hundred times (switched from opana to suboxone). If you're in withdrawl now (cold sweats, upset stomach, skin feelin crawly, legs shakey, ect...) and it's been at least 8 hours, you should be ok. I ususally always wait 8 hrs, I've waited 6 hrs after eating like 6 hydro 10s and then took subuxone and was fine. But once I only waited like 4 hours after a night of oxycontin and went into anticipated withdrawl. It was awful. I always wait until I can't take it anymore - and at the very least, 8hrs.