How long will literally one hit of meth show up in a lab urine drug screen ?

Wrong question.: It is illegal to use methamphetamine, and it is unethical for doctors to tell patients how to pass drug tests. If you can't afford to fail a drug test you can't afford to use methamphetamine. That notwithstanding there isn't a dirtier drug you could choose with greater risks associated with use. Just don't. And don't expect a any ethical doctor to help you do anything but quit. Please get help.