Saliva 1-24 hours, 48 hours max for chronic use

also I found this on another site when I was prepring for my screens.

Stay away from MJ for at least 24 to 48 hours. 72 hours is the best.
The day of the test you should clean your mouth big time, brush, gargle, and floss.
You should take Altoid Mints up to test time. They might ask you about mint intake, say "NO".
Wait to get the notice from your new employer on start time.
If they fail to call within 7 days, call them.

hope that helps