People who have been arrested—particularly those who haven't bailed out of jail or been released on their own recognizance ("O.R.")—want to know when they'll get in front of a judge. They want to know the charges they face, whether they can get out of custody (jail), and whatever else about the criminal process they can glean from that first court appearance.
Many states refer to the first appearance as "arraignment," while others use terms like "initial appearance." Some states will have both an initial appearance and arraignment depending on the circumstances. No matter how they describe it, they all prohibit law enforcement agencies from confining suspects indefinitely, without judicial oversight.
The timing of the initial appearance varies from jurisdiction to jurisdiction—and isn't always clear. (In fact, rules on arraignment and initial appearance can even differ from one city or county to another.) Some state laws specify how soon suspects are entitled to appear in court, while others vaguely ban "unnecessary delay" after arrest. Typically, though, a person who was arrested and is sitting in jail must get before a judge within 24 to 72 hours (with some exceptions). If the person is free on bail, the arraignment may happen later.
In both state and federal court, the initial court appearance is typically the point at which the court advises the defendant of the charges and certain constitutional rights, including the right to counsel.
The court may also:
Some states combine "probable cause determinations" with the arraignment. A probable cause hearing is basically a judicial check on law enforcement's authority to keep a suspect in custody. If the court doesn't find probable cause (sufficient grounds) to believe the defendant committed the crime—a rare occurrence—it must order the defendant's release.
In practice, government agents have a bit of slack—as long as they make a conscientious effort to get a suspect in front of a judge quickly, they're probably in the clear. And even an illegal delay in bringing a defendant to court probably won't invalidate a subsequent conviction unless the delay somehow contributed to it. (U.S. v. Chavez, 705 F.3d 381 (8th Cir. 2013); Morse v. U.S., 256 F.2d 280 (5th Cir. 1958).)
In a 2009 federal case, for example, FBI agents arrested the defendant for bank robbery pursuant to an arrest warrant early on a Friday morning. The agents began trying to locate a magistrate shortly after the arrest but couldn't find one who was free before Monday, which is when they ended up taking the defendant to court. In the meanwhile, the officers interviewed the defendant—during that interview, which was more than 12 hours after the arrest, he gave self-incriminating statements.
The defendant asked the court to suppress (exclude) his statements because he made them before officers had brought him to a judge. Federal law allows for the suppression of any statements made by a defendant before an initial court appearance if there was an unnecessary delay in getting him or her before a judicial officer. (Statements by the suspect within six hours of arrest are presumptively admissible.) But, because the court considered the delay between the defendant's arrest and first appearance reasonable, it refused to suppress the defendant's statements. (U.S. v. Harrold, 679 F.Supp.2d 1336 (N.D. Ga. 2009).)
If you've been arrested or charged with a crime, consult an experienced criminal defense attorney as soon as possible. An experienced lawyer can aid in trying to get you out of jail, guide you through the court process, and fully advise you of the applicable laws.