Norco contains a combination of acetaminophen and hydrocodone.
It is the hydrocodone component that is of interest when urine drug testing.
Many factors influence how long a drug remains in your system. Body metabolism, physical condition, state of hydration, age, frequency and method of usage will all affect your result.
The rate at which a drug is eliminated from your system is related to its half life.
Hydrocodone has a half life of around 4 hours and acetaminophen has a half life of around 2 to 3 hours. It usually takes about 5 to 6 half lives for a drug to be eliminated from your system.
With that in mind, and other factors as outlined above, for urine testing purposes you should allow around around 2 to 4 days to get hydrocodone out of your system and 1 to 2 days for the acetaminophen.