On a Urine Drug Test, THC will appear as a positive within 2-5 hours of use. How long it will still show on a urine drug test is estimated based on frequency of use, but does not take into account the weight and body fat of the marijuana user:1  One Time User may show positive for 1-6 days. 2  Moderate User may show positive for 7-13 days.ow long it will still show on a urine drug test is estimated based on frequency of use, but does not take into account the weight and body fat of the marijuana user: 1  One Time User may show positive for 1-6 days.