Brief Answer:
likely 3 to 4 hours
Detailed Answer:
HI, thanks for using healthcare magic
Vicodin HP contains hydrocodone bitrate 10mg and acetaminophen 660mg.
Hydrocodone has a half life of 3.8 hours and acetaminophen has a half life of 1.25 to 3 hours.
The half life of a drugs is the time it takes for the amount of drug to decrease by half in the system. It takes 3 to 4 half lives for a drug to be completely eliminated.
This means that it would take approximately 16 hours to eliminate hydrocodone and approximately up to 12 hours to eliminate acetaminophen.
Since your friend only took a 1/4 tablet, it should be eliminated in a 1/4 of the time-3 to 4 hours in most persons.
I hope this helps, feel free to ask any other questions