I'm sure glad I'm not responsible for answering this question for anyone, but it's fun to think about. It's an intersection of the demands of art and the practical business of running a theatre. But it's like trying to answer how long a novel or a movie should be. I think the really obvious answer is "as long as it needs to be" to tell the complete story, and that that's up to the author.

I think most modern writers are very cognizant of this, and they make sure that their works are of reasonable size (except for novels, because you can always write and publish more). For a play, I used to think that in general each page tends to be a minute in length, and this isn't necessarily wrong, it's just so wildly inaccurate that I think it isn't useful except as an extremely vague guess. It doesn't take into account the type of work being measured, and so many variables can go into how long a play winds up being at the end of the day beyond what is on the page. The point is that the author will use as many words as they need to in order to tell their story completely, except this can run into problems too. Things like "we have a 15 minute block for each short" or "we need/can't have an intermission" can affect it practically, but feedback for an author can impact it too - things like "I wish we got to see more of whatever" or "this scene/character/etc. doesn't advance the action" put the author in an unfortunate situation. All writing feedback should be taken considering the stake that the feedback-giver has in the work, and if that 20 page cut is the difference between seeing the work produced or not, that's up to the author. At the end of the day they're in charge of their writing, after all, and they can totally choose to judiciously ignore feedback even though the act of asking for feedback isn't the powerful position. Maybe those 20 pages are absolutely crucial to the experience they want to share, and they'll have to wait until later to get it produced. This is also coming from the perspective that the purpose of writing is to get it produced, while that is an unhealthy mindset I think for any author. They should write because they love it first and foremost.

Sure, yeah, art's important and the author's process is important, but I feel like they probably also have to advocate the most for their scripts, and the reasons theatres might want a play of a certain length are valid. A theatre company's job is to get an audience, and an audience never wants to sit through four hours of something. But at the same time, as ticket prices get more and more expensive, I'd feel a little annoyed as an audience member to pay $100 to see a 60-minute play. Ticket prices opens another whole conversation here, though. How do theatres break even and keep operating? How do they get enough money to pay their business and creative staff adequately? There's a sort of stereotype that lots of theatre-goers are old retirees (especially around Arizona, where we get all the snowbirds) and for them, money isn't particularly a problem. The same probably goes for tourist-based theatres too. It's super hard to get regular everyday "normies" to come see shows already, but higher prices for tickets don't help. But lowering prices probably wouldn't help either! I'm thankful this isn't my problem, and I have a lot of respect for the people who have to decide these sorts of things.

One reason that can justify long plays or plays with pricey tickets is if the play in question is good. I feel like most of the plays I've seen are actually pretty fairly priced according to what you get... but I don't know if I can say that about every play I've been in myself. I would be frustrated to see a good but short show if I paid a lot of money, just as I'd be frustrated to see a long but bad show for cheap. It's all about that balance. But also, everyone in your audience is gonna have different expectations and demands, so I guess the business's job is to please as many of those people as they possibly can so that they keep coming back.

I think living in the information age too plays an impact on how entertainment works, especially for younger audiences. Attention spans are getting shorter and shorter, and we see social media producing content that's very short but just long enough to give that dopamine hit. Life moves fast and patience is running thin across the board, so it's hard to sit down and enjoy anything for a long time. But then again, what do I know about this? It might not be as widespread as I think... think about how many people adore the Lord of the Rings Extended Editions. As far as I know, there isn't any empirical data about play lengths historically, though there probably is for movies. Either way, to attribute a tendency to doing short shows to societal psychology is well outside my wheelhouse, so I'll leave that there.

All that said, I can definitely say I've observed a very strong favoring for short plays in the last few years. Maybe that's what audiences want... but then again, how do theatre-makers know what audiences want? I've never heard of theatres asking for feedback directly from their audience, and maybe that would be a waste of time anyway. It appears to me (and maybe I'm wrong) that it's the people in charge of a production who work it in the way they think is good, and an audience may or may not agree whether or not they know anything about production. Nonetheless, I think it's undeniable that shorter shows are easier to produce. There's fewer lines to memorize, probably fewer characters/props/costumes/locations on stage, and best of all less rehearsal time to get through the whole play. And for community-level theatres I think those benefits are too good to pass up in favor of longer works, depending on the company-wide experience level of course. I'm sure length is a crucial component during any season selection.

Now, what about Shakespeare or other very long classical works? There's a running joke that an uncut Hamlet would be something like four hours long. But I've never seen an uncut Hamlet. Well, now that I think about it, I don't think I've ever actually seen a production of Hamlet. It's tons of words, sure, but I wonder if it's done particularly expeditiously if it will still take a very long time. I mean, probably... people who are a lot smarter than me say so and I tend to take their word for it. The Hamlet I was in a few years ago was cut, or if you prefer a juicier word, mangled. We called it "shotgun Hamlet" because it was "to be" 90 minutes and "not to be" four hours. This had a fair justification, it was intended to tour to schools. But how can you possibly take a masterpiece like this and cut out so much stuff and still sleep at night? It was the same deal when we did Love's Labour's Lost - entire characters were gone, speeches were sliced and diced, and worst of all I never got to say "honorificabilitudinatatibus" on stage. It's an interesting actor experience to take a look at the original text again, after you've memorized a cut, and see just how much was lost.

Cutting seems to be the trend across the board, though. Nobody does uncut Shakespeare because it's just way too long, but cutting it you have to decide what to keep and what you don't need anymore. Some say that every word matters, but the more you cut the deeper the gashes go and less material is left behind for actors to work with sensibly, and hopefully you don't have to go so far that things stop making sense. Thankfully I haven't been in that situation though. Thankfully I've never been in charge of cutting a Shakespeare play yet either. So to say it again, I don't really know what that's like. Anyway, just like Lord of the Rings Extended Editions, next time I hear about one of those complete 12-hour nonstop Histories anthology, you can bet I'll be there.

That's pretty much all I had to say about this. I don't know how long a play should be. It depends on your show, the story, where you're doing it, what your audience expects... So I think it's impractical to give a prescriptive answer. The better question to ask is "how long should this play be?" At the end of the day, if the play is good it should be worth the time, and if the play is bad... Get it over with quickly please.