It's possible. Typically, I advise clients that marijuana can still show up in your system for about thirty (30) days after you smoke. So hopefully you won't be drug tested until after this time elapses. You definitely need to stop smoking or you will violate your conditional discharge and end up with a criminal record and a driver's license suspension.
I agree with my colleagues. It has been my experience that allowing a probationer officer to know before the first test (or maybe when you are first put on probation) that there may be some residual metabolites from the last time you smoked prior to probation, they do not consider it a violation. However, if there is something active or if your second time comes out with it in your system again-that is a big issue.
This is not intended as individual legal advice and there is no attorney client relationship established by this answer. It is advisable that you seek individualized legal assistance. This is not a substitute for hiring an attorney.