Negative drug test results are quicker to obtain because they are taken at face value and considered valid without the need for further follow-up. However, positive test results often require further follow-up to test the dual samples provided, to confirm the chain of custody to ensure the process was valid (and the samples were yours), and to evaluate for any cross-reactive medicines you disclosed which may produce a positive result. I am not familiar with specific deadlines, but you may want to go to the test facility and check directly. (A call would not work, because the info would be considered confidential.)
This information should not be considered legal advice or a legal opinion, and it does not create an attorney-client relationship. The information herein is general and for educational purposes only. A complete consultation, including review of facts and documents and research is required for specific legal advice or a legal opinion. You should consult an attorney for legal advice for your particular circumstances.