The "I love you" knock has me choking inside

What exactly does a "long" knock sound like?

Yeah I was wondering the same thing. At first I thought it didn't really matter, you'd just go by the length of time between knocks. But then I saw the "be quiet", which would be indistinguishable from "cone here"...
- wouldn't be quiet b: Tak, tak, tak.
  and come here be: Tak, tak. Tak.
  My assumption is that dots have no pause after nock, while dash requires pause. Just like when someone uses Morse code underwater
  E.g.:
  U-571 Morse cose scene
I'm not certain but I'm assuming a short knock they remove their hand quickly after impact and a long hand they keep their hand pressed against the wall after impact. Or maybe the difference between knuckles and palm knocks?
If you do a long knock, you can kinda hear the delayed release from the wall if you listen closely.
like the engine of my car at idle
It's like Morse Code. It really isn't about the length of the sound, it's the spaces between them. A dot would have a short space after it, a dash would have a long space. So dot dot dot would be three quick knocks, dash dash dash would be three slow knocks.

They have 13 phrases. Could have kept to combination of 3 digits of dots and dashes and still have one slot left over.

.
..
.-
-.
-
...
..-
.-.
.--
-..
-.-
-.
--

If it isn't obvious, I don't have daughters.

Obviously we need to teach them Huffman encoding
They could also just use Knock Code which is a simple way to encode letters as knocks to send arbitrary messages. Most often used by prisoners since it's easy to learn.
Last knock kant be detected to be long or short (right?) so you have to redo it.
- The girls' codes do rely on that though
- You can just add a short knock to the end of every sequence, that should remove any ambiguity
3 and 7 are the same sequence. 8 and 11 are a sequence of 4
EDIT: I looked closer and realized these could be explained by simple typos; 3 would be .., 7 is not a typo, 8 would be ..-, and 11 would be -..

How ho you do that last long knock??

Yeah like maybe the one prior is just half cut off, so it's a a medium knock?

"come here" is the same as "30 min"?

Most languages have homophones where the meaning depends heavily on context. You wouldn't start a conversation with "30 minutes" and you likely wouldn't respond to "come here" with "come here" when "my room" is an option.
- The more difficult one is probably "come here" vs "be quiet". Unless there's some way to tell the length of the last knock those two sound the same, and they're both plausible responses to a "meet me" knock. "My room" and "tomorrow" have a similar issue, again being "we can meet, but you come to me" and "I don't want to meet" responses distinguished only by the length of the final knock
  But to be fair they're 11/9 year old kids, hell yeah for making a secret pseudo-Morse-code

I'd love to read the minutes from a "Super Sister Meeting"

How do you do a short vs long knock? I figured maybe they were talking about the pauses before the knock but then how would you know if something began with a pause or not?

Yeah for like "meet me out front", there's no real way to do that short knock

Is a long knock just a knock and a pause or some kind of rimshot/paradiddle?

Come here and 30 min are the same thing. I guess context answers that one.

The minutes are clearly to be appended to a meeting command, is how I read it. "Come here" alone makes sense. "30 minutes" alone doesn't.
- Of course. That's what I meant by context.
  I could have gone with "meet me out back" vs "come here in 10 min" as my example, but I'm not really trying to pick apart a children's code sequence, just enjoying it for what it is and having fond memories of doing similar things.

I would have changed the long and short to knuckle and palm strikes.

Wow are you really flexing on a kid
Haha I'm jk, that's a really good edit

Best I can do is two shaves and a haircut.

Shave and a haircut, two bits
- Haha. That makes way more sense. Thanks for the correction.

As sweet as this is, there's a part of me that'd like to see the ensuing chaos if someone added code for "I hate you" as --.

In my experience that is just slamming the wall

I had one of these with one of my sisters. I don't remember what any of the codes were.

This is super cute. Don't say a thing to them, but after they are gone from home, I would save it forever. Or maybe just leave it in the closet, and show their kids in about 20 years.

We did this with my brother

They share a wall, not a door