Indictments in Nevada can take hours or several weeks, depending on the case.
Most criminal felony cases never involve an indictment. Instead, the prosecutor usually submit an "information" to the judge alleging that there is probable cause to charge the defendant for a crime. Then later after the defendant is arraigned in Nevada (formally charged), the judge holds a Nevada preliminary hearing. Preliminary hearings are like a mini-trial where the prosecution has to prove that there is enough evidence to continue the case to trial.
In contrast, an indictment is like pre-arraignment preliminary hearing: The prosecutor amasses a Nevada grand jury of 16 to 20 people and presents evidence of the suspect's alleged criminal activity. If the grand jury votes that there is enough information to prosecute, the defendant will be charged. (Note that defendants who are indicted by grand jury are not entitled to a preliminary hearing following the arraignment: The logic is that the indictment served the purpose of the preliminary hearing.)
Prosecutors usually resort to using a grand jury only in felony cases with high stakes and that may attract media attention.
Grand juries versus trial juries in Nevada
The purpose of grand juries is to decide whether the prosecution has enough evidence to charge a defendant with a crime. Therefore, grand juries come at the beginning of a case, and they determine whether a case will proceed.
In contrast, the purpose of trial juries is to decide whether the prosecution has shown a defendant to be guilty beyond a reasonable doubt. Therefore, trial juries factor in only when a defendant decides to go to trial (which happens rarely). And whereas grand juries determine whether a criminal case will go forward, trial juries determine how a criminal case comes to a close.
Note that grand jury proceedings are conducted in secret, and the defendant's attorneys may not be present. In contrast, the public is usually allowed to watch jury trials, and the defendants' attorneys are permitted to take part. Defendants are allowed to testify during both grand juries and trial juries, but defendants are advised not to testify during grand juries since they cannot have their attorneys in the room with them.
Also, note that the state selects grand jurors and trial jurors from the same pool of eligible citizens. Similar to trial juries, grand juries have a foreperson, and they make their deliberations behind closed doors.
Finally, note that trial juries also go by the names "petit jury" or "jury".
Other grand jury facts
The prosecution is required to give notice to defendants it is trying to indict, and the prosecution must permit defendants to be present at the grand jury.
If a criminal charge that was made through an information gets dismissed, prosecutors can try to bring the same charges later on through an indictment. However, this usually occurs only in very serious cases.
The purpose of grand juries is to act as a "check" on prosecutors by preventing them from bringing charges when there is inadequate evidence. In reality, though, grand juries almost always vote to let the criminal charges proceed.
Fighting an indictment
A defendant's attorney may file a writ of habeas corpus challenging the indictment. If the court grants the writ, then the indicted charges may be dismissed. However, judges usually deny these writs in order to let the charges play out in litigation.