How much time does it take a drug test to come back a false positive?

Dont understand ?: Most tests are "screening" tests, and results from those can be available instantly on some tests - within seconds or minutes - or have to be sent to a lab where it is 1-2 days, depending on their volume, whether it comes on a friday before a 3 day weekend etc. If tests are positive, confirmatory tests are done and may take additional 1-3 days. If those are positive, they are usually NOT false +.