The reason they ask you about any over the ctuoner drugs you have taken in the past 72 hours is to see if you will have any false positives for recreational drugs. Every drug has its own time period that it is detectable for, most drugs are 2 to 4 days, marijuana can be up to 30 days but that is only with heavy use. If you smoked weed only once a week before, then you will most likely pass the test. If you were a habitual smoker for the past month before that though, then you run a good chance of failing it, if so get a system cleaner. If you are a smaller person with a high metabolism it will get out of your system a lot faster. If you are really worried I would recommend you start exercising and drinking a lot of water and tea until you have to take the test. School tests are known to be very cheap and inaccurate though and I knew someone who had to take tests at school and was a drug user, and would simply dilute their urine with 90% water from the bathroom sink and the school never noticed the tampering because they used a cheap enough test.