One hit wont show up if you don't smoke often. It takes a certain level of THC to show up in your blood for the test to be positive. Take Riboflavin 3000%dv and Niacin 300%dv the day of your test and drink mad amounts of water.
People say 30 days-----thats only if you been blazin ED or EOD for a good amount of time.
p.s. notice time you started this thread.. hmmm ironic??