A halflife of 3 hours means SWIY would have 1/2 of what SWIY took left in their system in 3 hours, 1/4 after 6 hours, 1/8 after 9 hours. SWIM
has heard it's up to 4 days before its not detectable but SWIM has passed tests they shouldn't have. In SWIM's opinion, there are a lot of things that can play into it, if SWIY system was clean before, metabolism, type of test, etc.
If SWIY has access in short time (nearby head shop) and money, SWIM would suggest urine substitution as the best method to pass a test if it is unmonitored. Otherwise its a crap shoot and SWIY very likely may loose.
But if this substitution isn't possible and the drugs
are already done, do the best SWIY can. If SWIY drinks too much water, the test will come back inconclusive and SWIY may need to repeat the test - this could be another chance if SWIY isn't going to be in the same situation on the re-test. Two inconclusives are usually considered a fail (and only one inconclusive may be considered a fail depending on the reason for the test, etc).