If someone smokes a joint or a few puffs on a pipe or whatever and doesn't do it again, the effects may be noticeable as "high" usually two, maybe three hours. Four is the outlier.

This was for tests of driving under the influence of mj compared to alcohol. Alcohol is worse, even if someone is somewhat impaired by mj.

After that time, the mj has a calming effect but not really a psychotropic one.

Saliva tests for thc are available in Australia and New Zealand, iirc.

The test MUST check for THC, not THC metabolites. Immediately after someone smokes mj, the body starts to break down the TCH to a metabolite that does not have measurable psychotropic effects, even tho it may stay in the body and slowly disperse. This is why there is no hangover and no withdrawal, other than psychological - the drug leaves the system slowly.

This is also the reason why blood tests are not good indicators, but are better than urine tests - which are the worst for THC b/c they are only measuring what is no longer psychotropic but has been metabolized and is being excreted.