Certain Opioids are affected by changes made to certain enzymes through certain foods and medications, this is true. The amount of potentiation that you will actually encounter is going to vary heavily though. Speaking from experience, using potentiators like Cimetidine (Tagamet), Grapefruit juice and the like might give you a boost of 10% - 15% at most, nothing groundbreaking.
From an enzyme perspective, the Clonazepam (Klonopin) is not going to have a major effect on what they do or don't do. The real potentiation is going to come from using a Benzodiazepine with an Opioid and the synergy that comes with using central nervous system depressants that work on different systems in the brain and body. As for more exact timing, all we can do is speculate.