I myself am going through a natural detox (cranberry juice and vitamin supplements which include B vitamins and niacin) because I also have a drug test coming up in the next week or so but I'm giving my body 20+ days to cleanse.
There is no evidence that cranberry juice, niacin, and other vitamins can expedite THC unloading. The only proven way to rid the body of THC is time and fat-burning exercise.

Make sure the temperature of their urine upon giving the test is between 92-100 degrees so the test result doesn't show up as inconclusive, in which case you will have to submit another test.
If a urine sample is outside the acceptable temp range, the collector is to order an immediate re-submit and under direct observation, as per regulations and protocols outlined by the DHHS. The collector would then process and send off both samples and indicate on the CCF (in the 'Remarks" space) that a re-collect under direct observation had taken place, and the reason(s) why.