I'm sorry for the delay. I uploaded an answer a while ago, but for some reason it did not go through.
You're not going to be able to see and speak to your son before he comes before the court. Only a lawyer can do that. You can, however, go to court and be ready to either post bail or take him home. You may also be able to speak to the lawyer who will stand up on his case. The clerk of the court will generally be able to give you a rough estimate of when he'll be brought before the judge.
An outright dismissal today would be highly unusual. And, in fact, an outright dismissal means that something is very wrong with the state's case, and it's never a typical outcome of a criminal proceeding.
However, even if there is no lawful basis to get an outright dismissal, the state of Texas does have special programs where a first non-violent offender can work the case off of his record. These are diversions/deferred adjudications. They consist of community supervision, fines, community service and anti-drug classes or counseling. THe defendant would have to stay out of trouble for the supervisory period and refrain from using illicit substances. If he does everything successfully, his conviction would be dismissed and he could honestly say he has no criminal convictions on his record.
Programs like this are at the discretion of the DA, but they are typically offered to first possessory marijuana offenders. The odds of his being able to walk away without a conviction are fairly good.