If there was no date on the citation (or no citation at all) there will like be no court date until the court receives charges from the city or county prosecutor’s office. The court would then create the case in their system and set a first date for your son to appear.
So, to answer your question, it could be several weeks or months and as much as two years from the incident date that charges are filed. In the meantime he should plan for the worst and hope for the best.
It’s never to early to consult with an attorney about your son’s options and I recommend that you all do so as soon as possible. I wish your son the best of luck in putting this behind him.