How long do opiates take to enter urine?

This is a question I can't seem to find answered anywhere: How long do opiates take to enter the urine. By this I mean how long after ingestion would a drug test yield a "positive" result. For example, if 40 mg of oxycodone (which I am asking about rather specifically) is ingested (intranasaly) at 2:00, at what time, if a drug test was administered, would the urine sample test "positive" for opiates? an hour later? a couple hours later? thanks.