"Oh, so there should have been a door there and isn't?"

There is! It's right over there; the star-side one is where people usually come to the establishment in the first place, and the back door opposite it leads to the backyard. But you didn't come through it.

He blinks and squints at it. "That had not been there a minute ago," he says, pouting. "...do people from all over the history of time come here, like in the books?" That could be a plot hook, someone from somewhen or something.

This one is more of a people from any universe situation.

"Oh there we go, that makes a ton of sense. How does that work?"

While you're in Milliways, time generally does not pass in your home universe; you return through the door when and where you left from if you came in that way to begin with. As long as the door is closed, it may substitute itself for any conventional door in any world, and someone may come through, hold the door to call over friends, spend any amount of time here, etc.

"—huh! And you say usually people come through doors and don't just appear, does that mean they sometimes do just appear?"

Yes, sometimes. Or through the lake, forest, or cave system in back.

"Do the same rules apply for them, usually?" Sip sip oh he missed this smoothie, it's so nice. "Original world paused, et cetera?"

It depends on why they have appeared, but more often than not, yes.

"That's excellent," he exclaims, grinning. "So what usually happens if someone who didn't come through the door then tries to exit it? —for that matter, how do people who come through the door, uh, come through the door? Like does Milliways disguise itself as a random bar in a seedy part of town or..."

Not as an entire building, no. The door substitutes itself for other doors - people may encounter Milliways on their way into the bathroom, out of a closet, through a hallway, etcetera.

"Just, like, randomly? Going about their day and suddenly boom they're in an interdimensional bar that pauses time?"

Yes. Some people can get doors slightly more volitionally than that but that's the standard case.

"Oh I bet I'm one of those people. But anyway yeah is there any sort of pattern for what happens if someone who didn't come through the door then tries to exit through it?"

Generally it will place them at their home or one candidate home if there are several and again some people can control details.

Once again he bets he's one of those people. It's just such a Mary Sue thing, really, most people never get doors and most of the ones who do only do so randomly except some special snowflakes can do it volitionally, and in the other direction too.

He sips some more from his smoothie and hums thoughtfully. "So then what's the, ah, usual thing that happens here? I assume there's typically more than literally just one person and you at a time?"

Usually, yes. I don't control the door, or the flow of time where it differs between non-interacting parts of the establishment, so I can't directly send you interesting people to meet, but someone should be along sooner or later.

"Wait, non-interacting parts of the establishment have different flows of time? How's that, just, like, you can spend five minutes in the bathroom and then come back here and it's been five hours for other people?"

Well, not if in those five hours they would have come to join you in the bathroom, but yes, more or less.

"Huh. If you don't control that, or the door, who does?"

The Landlords, but that's just a word referring to 'whoever or whatever it is that does that'.

The authors, then, gotcha.

"—hey, speaking of, you said the first drink is free, how do people pay for further drinks, is there some interdimensionally recognized currency of some kind? And for that matter do you sell anything other than drinks, can people have a dinner party here too?"

I sell any medium-sized nonmagical harmless nonliving object and can sometimes bend some of those limitations. I can take any currency and charge reasonable currency-dependent prices for things. Some patrons also choose to run up tabs.

"...that was pretty broad, do you sell, like, books? Clothes? Computers?"