I can't speak for the specifics on this medical test. But generally speaking THC byproducts are detectable up to a few months after smoking, but that assumes you had a continuous habit before you stopped. If this was the only occasion the test should be negative rather quickly.
I once smoked the day before a urine test was taken and this came out negative, although I got a verbal comment that my values were close to the cut-off. This was 20 years ago, so don't know if the tests have changed.
Maybe consider seeing a friendly doc for a quick private test first if you want to be sure. I'm not going to comment on the ethics & morality as I assume you will get feedback from others on that.
Good luck!