Perhaps it is unethical and immoral to use anything other than a carbon monoxide testing machine (it looks like a breathalyser) to test for smokers, assuming that this is acceptable in the first place - perhaps for insurance purposes.
However these machines are expensive and it is cheaper for employers to use a cotinine/urine test. No one seems to use a nicotine/blood plasma test now.
The nicotine level in the blood will take around 24 hours or longer to fall to the level of the background 'noise'. To explain: smokers test out at from 10ng/ml to 50ng, and vapers normally test at a max of 40ng. Everyone tests positive for nicotine as it is a normal part of the diet. The background level is about 1- 2ng, for a non-smoker. Living with a smoker or eating very large amounts of nicotine-containing vegetables such as eggplant/aubergines might take that level up a bit.
Unfortunately the main nicotine metabolyte, cotinine, is easily detectable above background levels for several days, possibly two weeks. There are said to be ways of flushing it by certain dietary or pharmaceutical means (google: drug test pass kits).
If you need to pass your test then the only reliable way is to go cold turkey for at least two weeks, and make sure you drink plenty. Or choose an employer that has some respect for human rights or is intelligent enough to use an insurance company that knows the difference between smokers and other leisure users of nicotine.
Admittedly, it is a tough thing for insurers to decide on - look at it this way: a CO monitor detects smokers, so they can be excluded if that is acceptable. However any form of nicotine or cotinine test cannot tell you if the subject is a smoker or on NRT for example. And since there is a 95% probability or higher that a subject on NRTs will return to smoking, it is not unreasonable to consider them a smoker.
As yet there isn't a test that shows the subject is a Snus or e-cigarette user and therefore has little likelihood of any elevation of risk over a non-smoker.
The main issue for employers/insurers is the fact that subjects who register a strong positive in the cotinine test are either smokers, or on NRT and will therefore almost certainly be smokers again very soon. The likelihood of positive tests being for Snus or ecig users must be extremely small, currently.