If you get into an accident and kill someone, they do drug screening. If you have metabolites of weed in your whiz quiz, you will be charged with OWI and manslaughter (in my state.) It varies from person to person, but it can take up to a month (heavy user) after smoking weed to pass a whiz quiz. If you smoke once or infrequently, most people can pass in a week. The reason it takes so long is the metabolites are stored in your body fat.
Yes, but such tests still can’t determine if you are intoxicated. All they can say is if you may have consumed marijuana sometime in the last 2-6 weeks or so. Obviously, you don’t stay intoxicated for 2-6 weeks after ingesting marijuana, so the tests can’t actually tell us that.