This is speculation on my part, but I suspect that in the the times that live theater was a popular form of entertainment, rather than something for the elite, people might have been likely to wander in and out at will. I can easily imagine that in Shakespeare’s day they weren’t controlling entrances and exists based on when the play was starting and ending. Certainly, if a play was taking place in the public street, and performers were passing the hat, people would wander by as they pleased.
Bill Bryson describes in one of his books how British nobs would often send servants to sit in the audience for the first act or so, then fill them in when the nobs got finished with dinner and decided to show up.
Dunno about plays, but people watched stage shows that way. You can come into the Muppets at any point, and keep watching until you run out of time. Jumping over the seats to get closer to the stage as the audience cycled out.
But could you watch stage plays that way? I was born in the 60s and don’t remember double-features being common - but I absolutely remember getting into the theater after the movie started* and leaving when the next showing got to “where I came in”. But that was when there would be a showing every 2-21/2 hours with only a short time between showings - they didn’t make sure to empty the theater so they didn’t need half an hour or so. If you missed the beginning of the 5pm show, there might be only a 10 minute break in between shows. Did that ever happen with stage plays , that there was a short enough break between performances that people might stay to see the beginning they had missed**?
- It wasn’t intentional, but it wasn’t always avoidable when taking the bus to the theater.
** I know that wasn’t possible immediately pre-COVID. Even if they hadn’t emptied the theaters, a matinee at 2 pm ish would be followed by an evening performance at 8 ish - too long to wait around.
There’s one specific point in theater history where people could, and probably did – the medieval mystery play cycles in cities like York, where there would have been multiple performance sites around the city and multiple guilds performing throughout the day, moving from station to station. Each guild had its own play (often related to their occupation in some way, so you’d get, for example, the bakers performing the Last Supper play and the Fishers and Mariners performing Noah’s Flood) which they’d perform over and over, and this would all have been in the public streets without any ticket-taking, so audiences would have been free to come and go.
But it worked because 1) the individual plays were super-short, so actors could perform the same one multiple times throughout the day without getting exhausted; and 2) everybody already knew the plots and how they fit into the larger narrative of the Bible. Once the commercial theater finds its stride in the Renaissance, it’s a totally different model. (They may, as @Ascenray suggests, have let you in if you arrived late in Shakespeare’s day, but you’d be out of luck if you missed the beginning of the play – only one performance per day. Titus Andronicus on endless loop is not something you can reasonably ask your actors to do.)
In Vaudeville days, the acts were discrete, so you could come and go. Indeed, being the last act was considered a terrible position to be in, since the audience would be leaving while you were trying to perform.
We used to go to movies late, but that was a function of how we had to eat dinner. The early show began at 7 pm. We didn’t start dinner until 6 or a little later, when my father came home. It took 15 minutes to get to the theater, so the time frame was short. I often missed the beginning (biggest miss was when we came in the middle of Blue Waters, White Death, but that was a documentary, so it was easy to pick up).
I credit this for developing my sense of story. I usually had to figure out character relationships on the fly.
Again, pure speculation, but maybe there were multiple companies that performed in sequence. Like at the Ren Faire. A half a dozen acts might be assigned to a single stage and the big dramatic shows might play only once or maybe twice, but shorter acts might have cycled through among jugglers and acrobats and such? I can’t imagine it would have been economical to use a theater for only a couple of hours a day.
There would have been some pre- and post-show entertainment (plays typically ended with music and / or dancing, and were often followed by a bawdy comedy sketch called a “jig”), but only one full-length play would have been performed in a day. Don’t forget, the company needed time to rehearse as well, and these were outdoor theaters with natural lighting, so performances could only take place during the daylight hours.
Not really with anything that had a narrative. Certainly if we are talking about things like Broadway-type shows there would normally be no more than two shows a day, matinee and evening, with several hours between shows.
When I venture out to the movie theater it will be for off hour performances and they seem to allow you to sit through multiple showings now. People will come in mid-movie and still be there whenever I’ve gotten around to leaving. Maybe they shoo everyone out after the prime showtimes but it doesn’t seem like they care when theatre is mostly empty anyway. That’s pretty much the same as when I was a kid except the showings don’t run right into each other without a break, there’s always some blank screen time now.
To put a finer point on this, I’ve done a lot of community theatre. Most shows run for about two-and-a-half hours, including a 15-minute intermission. Depending on your role, you might have to be “on,” and in-character, for up to five hours, on matinee days. Such days are difficult, because you’re doing two shows in one day, and they are exhausting.
On matinee days–often Saturdays, but sometimes Sundays–we’d have a call time of noon for a performance starting at 2:00 PM, and lasting until about 4:30 PM. Then we were free–but we’d have a call time at 6:00 PM for a performance starting at 8:00 PM. So we might have 90 minutes to get and eat a meal from somewhere (remember, we’re community theatre, and our budget didn’t typically include cast meals). The local pizza joint, Subway, and Burger King got a lot of business from us on matinee days.
Professional actors may not be quite as tired as we are after such a day, but I’m sure they’re still exhausted.
Certainly in the 18th century people - and especially the posh folk in their private boxes - would wander in to the opera fashionably late, as the main purpose of being there was to see and be seen. Also, performers would sometimes repeat popular arias when egged on by the crowd - they didn’t repeat whole operas but the highlights sometimes got an encore performance. It was a noisy, raucous affair.
In the 19th century it became more about shutting up, facing front and actually watching the performance, especially once Wagner got involved.
This is interesting, but Bryson isn’t a reliable source of information. He blithely repeats urban legends and other things he has been told without further examination.
If this was Great Debates, I wouldn’t cite him. Seeing how it isn’t, and is actually just a hijack of a thread in Cafe Society…
I remember a lot of cartoons and comics featuring Truant Officers. Even as a kid in the 60s, I had to ask my parents about it. Anybody here ever see one (or another staple, The City Dogcatcher) in real life?
Come to think of it, maybe a lot of Lazy Comedy Writing has used tropes from decades before, so it’s always way behind the times. Think of all the bottom-shelf sitcoms where the humor is based on 50s clichés… (“Ha ha, look at Jim Belushi, he can fix a car, but not dinner because he’s a guy!”)
(Hmmm, at the school I teach at, I can get those fun Graphics people to print any title I want on my business cards. I was going to go with “Hallway Monitor”, but I’m betting the college doesn’t already have a Truant Officer…)
Our town has a truant officer. I spoke to him on the phone when he called to ask why my son hadn’t been to school. I explained that my son was a attending a private school, which should have been obvious after the public school had sent his transcript there.
Most cities and suburban towns have animal control officers. I don’t think they ride around in a truck with a big DOG CATCHER sign on it though.
The Truant Officer showed up a lot in Little Lulu comics too. His name was Mr McNabbem. 
In 1878 “HMS Pinafore” was badly reviewed as being long and slow, after the London first night performance ran to nearly double time due to applause and repeats. After the first couple of performances, the audiences settled down and let the show run to schedule.
Tangent: Shows like that started with an overture, to give the audience time to settle. I suspect that, lacking electricity, electric bells, and public address systems, the theater actually used the orchestra to signal to the audience that they needed to take their seats.
Thank you for answering a question I’ve wondered about for some time. 
Your city still has dog pounds, right? Well, how do you suppose stray dogs end up there?
I don’t think the local dogcatcher trucks have a sign on them, but they’re very distinctive-looking trucks.