For example, if I say a word or phrase and it lasts 5 seconds in normal unprocessed state. If I run that recording through silent subliminal script, will it last 5 seconds or does it decrease in duration?
If it does decrease in duration, how can it be understood, because decrease in duration means the utterance has been sped up, maybe the sped up version might be too fast for the mind to understand.
“Silent subliminals” are the same duration as the original audio, but are incomprehensible … "Silent Subliminal" messages revealed - YouTube
If it’s subliminal, obviously you can’t hear or understand it. 
If one can’t hear it, doesn’t necessarily mean that one doesn’t understand it.
It would be something like spotting with the corner of your eyes.
If you can see it (or hear it) it’s not subliminal. Maybe a visual analogy would be “reading” a book from across a football field.
And if you can understand it, why all the questions?
“I’ve created a subliminal message to help you stop smoking. Play this message in your headphones all night for several days. It should not keep you awake. See how it goes.”
You just made a Silent Subliminal Message.
If you want to carry it to the logical extreme, make a fully produced (short) message and let the subject hear it. Then “encrypt it” and hand it to them. There doesn’t have to be anything actually on their disk or tape. They need to be perfectly clear what’s expected going in.
You can’t force someone to do something they don’t want to do. That playing stuff in the background coercion business doesn’t exist.
Koz
Did you know that all LCD screens and similar screens don’t actually produce pure yellow color, they rapidly turn on and off or change the intensity of red and green pixels, you don’t see this because your brain is not fast enough. So your brain hallucinates the yellow color.
Similarly, it is not necessary for you to actually be consciously aware of something to understand it, how many times has it happened to you, when you are in a 1 on 1 conversation with a person, your concentration is on what the person is saying, but something about their body language gives you even more insight into their mental state, but you don’t remember paying attention to their body or their body is obstructed behind a desk.
Similarly in poetry, you may see some words, but they suggest something which is not the sum of the words.
Your analogy of reading a book from across the football stadium is not apt, more fitting analogy would be, you are in football stadium, the teams are playing, the crowd is booing and cheering, but someone left their bluetooth speaker on and playing songs through it, you don’t hear the songs over the booing and cheering but you are reminded of a song, which was playing through the bluetooth speaker. It does happen a lot. You think the song you are reminded of just popped into your head without any stimulus but it was actually because it played through the bluetooth speaker.
So you are saying it is more like the power of suggestion rather an actual stimulus? If the stimulus, however low in intensity is similar to something, I’m sure it is bound to evoke some response, regardless of whether it is due to someone believing such things.
Since half or more is happening inside someone’s head and is affected by environment, reverse-engineering and meaningful, reliable product testing doesn’t exist.
Directly interacting with the particular subject and setting up expectations as above is much more reliable and predictable.
Koz
The duration of an utterance in a silent sound subliminal message can vary depending on the specific message being conveyed and the techniques used by the creator of the subliminal message.
In general, subliminal messages are designed to be presented at a speed that is too fast for the conscious mind to detect, but slow enough for the subconscious mind to register. The duration of each message can vary from a fraction of a second to a few seconds.
Some creators of subliminal messages use techniques such as time-stretching or pitch-shifting to modify the duration of the utterance and make it more effective. The goal is to create a message that is easily perceived by the subconscious mind but not consciously detectable by the listener.
It’s important to note that the effectiveness of subliminal messages is still a subject of debate and there is no conclusive scientific evidence that they are effective in producing long-lasting changes in behavior or attitudes.
It’s easy to mix a quiet sound and a loud sound with Audacity. And like I said in the other thread, later you can subtract-out the louder sound to reveal the secret message which makes it more fun, and it proves there is really something there. (You can’t later subtract-out the crowd sound from a football game because you don’t have the bit-identical noise-only without the inaudible music mixed-in.)
FYI - MP3 and other lossy compression works by trying to throw-away sounds that are masked by louder sounds and other sounds you can’ t hear so you might want to avoid MP3 or other lossy compression.
…And I’m still immune to subliminals of any kind! 
Most of us here are skeptics, but we’ll help you with the technical details if you tell us exactly what you’re trying to do.
That’s only valid for images: not applicable to audio.
(25x speed, @96kHz)
Do you know how or why the mind or ear is able to hear a masked word or phrase?
I tried this method. So what I did was I made affirmations and I imported rain sounds into that project, I reduced the volume of the affirmations to -20dB. I saved this file with faint affirmations and rain sounds.
Then I opened that file in a new project, and I again imported the rain sounds, I panned the faint masked affirmations to the left, I inverted the rain sounds and panned it to the right, saved this as a stereo file but when I play this file, the inverted rain sounds are not canceling the rain sounds masking the affirmations.
So I understand this, you have masked message on the left and inverted rain on the right. If you presented this in headphones, I would expect the masked message to be in the left ear and the flopped rain on the right ear. Why would they cancel?
Try this. Select the track. Tracks > Mix > Mix Stereo down to mono.
Koz
Even at the Vons Grocery Store when they play "“Buy Cheereos, Buy Cheereos, Buy Cheereos” behind the music?
Are you sure?
“John Cheereos, please pick up line four. John Cheereos, line four.”
Koz
I thought human ear would work in the same way as in Audacity and they would cancel out. If mix stereo down to mono, I’m sure rain sounds will cancel out leave the masked affirmations.
How long should I listen to silent subliminals to notice any effect? And what kind of experience will I have to know that it actually had an effect?
Sort-of related… If you invert one side of a stereo recording the out-of-phase bass sound waves will be (mostly) be canceled in the air when listening to speakers. (This is most obvious if you have speakers that put-out good bass.)
The other frequencies cancel more randomly because of the shorter wavelengths and the way they bounce-around the room. It won’t sound like “cancelation”. And you’ll hear some weird phasing/comb filtering effect and usually some “stereo widening”.
…Bass is usually “mono” (the same on both sides) and that also helps with the cancelation. Sounds that are on only one side won’t be affected.
But when you listen on headphones where the left & right soundwaves don’t mix it will sound perfectly normal. Your brain doesn’t cancel the left & right signals.
A scientific experiment would involve multiple trials and multiple subjects, some subjects getting a “placebo” (no actual subliminal) and then statistical analysis of the results.
…If I buy Cheereos sometime this year, was it because of Koz’s subliminal? 
Of course it’s impossible to know, and overt advertising is obviously a lot more effective than subliminal/suggestive advertising.
And that’s the exact place you sail right away from the engineers and developers. All we can do is make sure the process you’re using to generate the message works.
I was very firm about being able to encode and decode the message when Steve TF made his subliminal encoder. None of this generating an affirmation message by magic business.
I posted that my next effort is recording the sound at the headphones or earphones. If I can do that, then engineering can guarantee the message is reaching your ear. Past that, it’s up to you.
Koz