I believe it is possible to test for them for up to three days unless you have kidney problems. HOWEVER, they would only do this is they had reason to suspect usage because its expensive, I tripped throughout the last 4 months of my probation.
Psilocybin may be traceable for 3 days but the point I was making is that they don't actually test for psilocybin, som although it may be detectable the tests don't actually show any thing when psilocybin is present.
I have found in my research that only specialized urine tests can detect the use of shrooms and only up to 1 week after consumption, i dont know about the hair and saliva tests.
I saw a phamplet back in the early 90's and shrooms were the only substance that DID NOT HAVE A TEST!!! Proven fact that 90% of what makes you trip on shrooms is gone by the time you come down. Substance leaves through your urine, tears and sweat. Shamans in Russia actually saved urine to get additional trips. Unless they get you while your tripping "AND" know what to test for you're safe. I have to random test once or twice a month and have tested the day after without trouble. ENJOY!!!