How long after arrest do I have to wait to find out what the charges are?
For suspects who are in custody, some kind of court appearance (usually an "arraignment" or "initial appearance") must typically occur within two or three days. At that court appearance, the government presents the charges against the defendant. The charges are normally subject to change, though. For example, a prosecutor might not make a final decision on charges until after a preliminary hearing, which can take place more than a month after arrest.
For more detail on the first court appearance and what happens at it, read about the arraignment process.