That reminds me of the awesome discussions I often have with hypnotists about the possibility to make someone under hypnosis jump off a building. Surprisingly, only very few give the answer you’ve given here.
Anyways, we don’t know how large and diverse the testing group is, what the environmental conditions are and how true to the testing protocol they are. The variable here is the one thing we simply don’t have the capability to measure: how long it takes for a person’s subconscious to process the message. Ignoring for a moment your very important distinction of how aligned the message is with the current dominant programming, there is a much simpler question of how fast it would process any message. For some, one hour of listening would take one hour of processing. For others, two hours or 30 minutes. I mentioned this somewhere higher in this topic, I believe. We would need to give our subconscious the time to “digest” the messages before we feed it more. Hence the rest/recovery period.
But until we can actually measure that, we’ll likely work off the conservative number. One that works for even the slower minds among us. Even though some among us can listen to three overlapping subliminals for half a day (another thread investigated this phenomenon), the vast majority would likely have better results listening up to 12 hours a day and not at night.