The only answer to this question that you should approach with seriousness is "when you begin to feel serious Opioid withdrawal". It's not based on any kind of specific time frame really, given the fact that everybody's physiology is different. Further complicating this situation, Opioids aside from Heroin/Morphine like Fentanyl and its analogs are now extremely common, so whatever shaky ground we previously had with which to guess from, is pretty much gone.
I'm closing this, because there are a ton of other threads open dedicated to the exact same question and the answer is always going to be the same.