What are the cutoff levels for marijuana on a probation test

What did the court stipulate ?

Zero. Its actually illegal under Federal law which supersedes any local laws. Any detection is grounds for a fail.

If this is the first test, going on to probation, they will normally understand past drug use ( if you were arrested for drugs) and take into consideration, date of arrest, (expecting you to have stopped once arrested)

If later into your probation, any usage will be a failure.

So there is no accepted allowance in reality,

The important thing is your tests need to verify a diminishing level of marijuana (or any substance) in your system over time. You will be/or have been asked on your first visit of any drug history, or meds prescribed by a doctor. If you have not disclosed any usage and it's found in your system you are in deep trouble.