Heavy, or one off / occasional use ?
Cannabis is fat soluble, so over sustained regular use it is deposited around the body and can take several weeks, too a month to be excreted. In practice this only occurs in heavy regular consumers of cannabis, usually the concentrated forms such as skunt, and for most irreglular or occassioanl users THC will be excreted much quicker.
The saliva drug test kits currently detect at 12ng/ml THC Cannabis
All urine instant tests cut off at 50ng/ml while lab confimations normally test to just 15ng/ml
Instant urine tests will mainly detect for 3-5 days after light use. For tests to remain positive longer than 5 days suggest either heavy previous use, or re-exposure.