My name is ***** ***** I am an experienced criminal lawyer.
Your son's Constitutional right to counsel doesn't attach until his arraignement. That's when he comes before the judge and the charges against him are read into the record and he's asked how he pleads.
In most juridictions jail cases will be provided with a public defender for the arraignment. But if your son is not provided with a lawyer for purposes of his arraignment he needs to plead NOT GUILTY to the charges. That keeps all of his rights open so that he can consult with a lawyer on his case. Once he's pled not guilty, he can let the judge know that he is without the funds to hire a lawyer and ask the judge to appoint him a public defender.
The reading of his rights lets defendants know that they do not have to answer any questions about the incident they are going to be charged with until they are able to talk to a lawyer. The police do not provide him with a lawyer if he doesn't have one. But he could have refused to talk.
If he didn't understand his rights and he made incriminating statements that could hurt him in court, his lawyer can eventually get a hearing on that issue to try to keep any statements improperly obtained by the police from being used against him at trial.
If you can bail him out now, that's something you can do. Otherwise, he'll have to wait until he comes before the judge on Friday, at which point if he doesn't have a lawyer he can ask for one as indicated.