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.
Vaping can simply be seen as smoking but with no requirement for any tobacco. New vaporizing devices called electronic cigarettes produce clouds of vapour, or mist, not real carcinogenic-filled smoke. Essentially, the e-cigarette replaces combustion with vaporizing. The health benefits of this relatively simple switch are astronomical.