It also depends on how long and how frequently you've smoked. If it was one hit, one time only and ever, should be out of your system for a urine test within a couple weeks, if not days. If you're asking how long you stay high off one hit...depends on the weed and how often you smoke. But, usually not very long.
Manufacturers often design e-cigarettes to look like regular cigarettes, but they contain no tobacco and don't require a match -- or any flame at all. An e-cigarette is a battery-powered device that converts liquid nicotine into a mist, or vapor, that the user inhales. There's no fire, no ash and no smoky smell. E-cigarettes do not contain all of the harmful chemicals associated with smoking tobacco cigarettes, such as carbon monoxide and tar.
In the first five minutes, the traditional cigarette users had elevated levels of plasma nicotine, carbon monoxide, and a higher heart rate. The vapor cigarette users did not experience a marked increase in concentration or heart rate. They did however suppress nicotine/tobacco abstinence ratings. Another study by the University of Athens 3 examined the acute effects of vapor cigarettes on the lungs.