I think that is a great point.
Also,
The process of integrating a subliminal is one of receiving and integrating a message. It’s probably better to use a learning-based metaphor rather than one based on physical-transfer.
Remember how when you were in school there were people who grasped certain subjects very, very quickly? They only needed to be told or shown once and they were already getting it. Then there were those who needed more time and repetition to feel competent and comfortable with the subject.
15 minutes seems to be okay for me right now. And I want to keep things simple. So I just play it for 15 minutes every other day and let it roll.
Maybe one day the variable lengths will become official and 3-, 7-, and 15-minute versions of a track will come with each purchase. At that point, I’ll try it, but for now…I seem to be just staying with the 15.