Thanks for the chance to help. I am an attorney with over 12 years experience. Hopefully I can help you with your legal question.
The 6 months is a key window. The ACD you mention is a form of "deferred adjudication". This allows an individual to avoid a criminal
conviction if they meet the terms of the agreement. So, for your son, if he avoids criminal misconduct for the 6 months, the charges will be dismissed. He will NOT have a conviction on his record for either.
That is a good thing
On the other hand, a simple arrest in this window can create what is known as a vacation hearing where the judge can, basically, find him guilty of the subway charge and drunk in public charge...and this can happen with just an arrest...before he even is found guilty of the new charge.
That underscores the importance of avoiding arrest if at all possible.
Now...on to your question. What if he is arrested?
One of the most important right your son, and really all citizens have is the right, under the 5th Amendment of our Constitution, against self incrimination.
If he is arrested he should invoke that right.
He should say NOTHING to the police (other than identifying information...he needs to give them his license..but he does not have to answer ANY questions).
In my years as a prosecutor and defender, the vast majority (something like 90% or more of all cases that went to trial
had a statement by the accused. And it the vast majority of those cases, the statement was used at trial to prosecute the accused. SO the best thing anyone can do is arrested is to hand over their drivers license and NOT SAY ANOTHER WORD. Not one.
Now, if they want to put him in jail, they have to give him a chance to see a judge to request bail. During the week this happens the next day. Over the weekend it will happen on monday. He will be given the chance to call a lawyer or someone who can find a lawyer for him. IF he can not find a lawyer, then the best thing to do is wait for the bail hearing and ask the judge to allow release. For minor crimes suspects are released with no bail or very small bail amounts.
Again, the most important thing he can do, and really that anyone can do, if arrested, is to not make any statement at all.
They will be given a chance to see a judge and apply for bail as well as the chance to call someone to help find a lawyer.