How long does it take to lower opiate tolerance so that I don't increase to an unhealthy dosage?

It depends. Tolerance is defined as the adaptation to a drug resulting in reduction of effect over time. Tolerance to side effects develops more quickly than tolerance to pain relief. It is thought that tolerance to the pain relieving effects of an opiate occurs rather slowly. In general a 10% increase in dose is required every year in order to maintain the same pain relieving effect.
Variable. Opiate tolerance develops over time because of the activation of certain enzymes in the liver which metabolize the drug. There is also a genetic component to opiate tolerance with genes being tied to rapid and slow metabolism.. The answer to your question is that it is patient specific but in the pain management arena we rotate opiates so that tolerance does not become an issue.