What sets the length of a courtroom trial? How does the judge determine what’s a “right” amount of time so it doesn’t go forever?

>I imagine lawyers must want to try to throw in the kitchen sink and have tons and tons of witnesses going down every rabbit hole,

It’s actually the exact opposite of that. Prosecuters and defense attorneys generally prefer to use the least amount of witnesses possible because:

(a) Witnesses are people and people are unreliable, especially when put on the stand and are expected to tell a very specific story in front of a room full of people with the added pressure of telling your version of the story in a way that is convincing.

(b) Witnesses are subject to cross examination by the opposing attorneys. Most witnesses are just regular people who have never been on the stand before and they lack experience in providing testimony. Meanwhile, the opposing attorney has a ton of experience in cross examination and can easily frame together a series of questions that will get the witness to contradict or at least cast doubt on their own testimony. This can be especially hurtful to the prosecution and beneficial to the defense.

(c) Even expert witnesses who are brought in to testify about a very specific aspect to the case can be tripped up by an experienced attorney during cross examination. On top of that, expert witnesses can be very expensive, and if any level of govt is involved as a plaintiff or defendant, that cost is passed on to the taxpayer, so it’s important that these types of witnesses are used as sparingly as possible.

Judges have a lot of leeway when deciding how their courts should be run. But you might be imagining things like TV shows or movie depictions of trials.

Trials are very “scripted”. Lawyers don’t get to introduce surprise witnesses, they cannot suddenly drop in new evidence. There are usually things like pre-trial conferences, depositions taken from witnesses, etc etc that both sides participate in separately and together. By the time the trial starts, they know exactly who will be called to witness and probably have a really good guess as to how the witness will respond.

Judges take a VERY dim view if they think a lawyer is wasting time. By the time the trial starts, all evidence and witness statements are ALREADY ON RECORD. A witness changing their statements during trial will be, at a minimum, scolded by the judge.

Pretty much the facts of the case (as far as possible) will already be agreed to by both sides before trial. The lawyers argue their case but they cannot simply add to facts without giving the other side an opportunity to review and examine before trial.

99.9% of the time, lawyers AVOID pissing off the judge. In fact that might the biggest rule for trial lawyers. The defendant might be facing the judge and trial for the first time but lawyers have to deal with the same set of judges pretty often. Piss off the judge enough and the judge can request for a sanction on the lawyer. Few lawyers will risk this since this is their livelihood not to mention their professional, sworn duty.

The judge doesn’t directly set a length for a trial, by saying “this trial will take 10 days” or something like that. The length of a trial depends on how complex the case is. If you have a case about a car crash where one driver is going to testify that the light was red and one driver is going to say it was green, that probably won’t take very long. If you have a financial case where the evidence includes thousands of pages of bank records, and accountants need to testify about what the records mean, that can take a very long time.

The judge influences the length of the trial by ruling on what evidence comes in. Usually, these rulings depend on whether the evidence violates some legal rule meant to ensure reliability. But the judge can also exclude evidence that isn’t very important compared to how much time it would take up, just to speed up the trial and keep it efficient. In federal court, the rule of evidence for this is Rule 403, which allows a judge to exclude evidence based on “undue delay, wasting time, or needlessly presenting cumulative evidence.” A judge can definitely favor one side or the other with these rulings, and the side being ruled against often feels like that’s what’s happening!

Most of the rulings are sorted out before trial, so by the time trial starts everyone has a general idea how many witnesses will testify and how long their testimony will take. The judge and lawyers give a “time estimate,” but it is not a hard limit. The trial will go as long as it takes to finish.

During trial, the judge can also control the courtroom proceedings and can stop questioning of a witness or argument by a lawyer, if it’s getting repetitive and is no longer productive. But judges generally let the lawyers ask as many questions or argue as long as they want, since the wrong ruling might get the case thrown out on appeal. The lawyers are also trying to persuade the jury, not bore them to death, so they have their own incentive to get to the point.

Also, the time estimates are frequently wrong. Trials are chaotic and unpredictable. Another commenter said that trials are “scripted” and there are no surprise witnesses. I disagree. It’s true that you don’t see some important, star witness burst through the doors like on TV. But crazy stuff happens all the time. Witnesses change their testimony or may not show up at all. New evidence might be discovered in the middle of trial. Testimony that was expected to take 20 minutes might take two days, because the witness is difficult or the lawyers have some point to make. And so on. A trial involves many moving parts, including multiple human beings with conflicting goals and personalities, so no one person is in total control.

Source: am a trial lawyer.

Before the trial takes place, there’s a lot of maneuvering on both sides to determine what is officially “evidence” in the case. Testimony/objects/information/etc. can only be presented at trial if it is first recognized as evidence. This is often a decisive phase for a trial. A drug possession case doesn’t really work if the drugs or police testimony are barred from evidence for some reason. It also means that the kind of dramatic surprises you see in courtroom movies are very rare – a surprise witness better also be a surprise to the lawyer who is calling them, or else the judge will ask why no one mentioned this during the months of pre-trial proceedings.

So by the time a trial starts, there’s general agreement on who will testify and even what they will say. When putting together this list, the judge can exclude evidence they think will be irrelevant, but there’s usually a bias towards being very comprehensive and precise, so everyone accepts that a thorough trial may take a few solid days. The trial doesn’t have an explicit time limit – it takes as long as it takes. There’s also no real incentive to intentionally stall – if that was going to be your tactic, better to avoid a trial altogether!

>Seems like this must be a very judge-dependent and judge-controlled thing?

Not really. There’s a phase before the trial begins called ‘discovery’, where the attorneys make a list of the evidence and witenesses they intend to show to the jury. As others in this thread have pointed out, the dramatic trope of the surprise witness is completely not allowed, and can cause a mistrail, and often results in disciplinary actions for the lawyer who fails to disclose all the evidence in the case.

Getting back to your question, the judge examines the evidence that each litigant / counsel wants to present, and budgets sufficient time for it to be shown. But, there are rules as to what kinds of evidence is admissible and pertinent, and a lawyer will waste the court’s time at his client’s peril, as well as his own.