Jeff ran the kundalini and schumann presets on separate generators for 8-12 months straight. So there is not a set limit. Just as long as you need. But remember entrainment happens when there is a continual tapping on the issue and not just a 1-2x run through.
My pea little mind thinks of enTRAINment like this - a training of the organ or body part to nudge it back to normal. A consistent tapping of a frequency on the organ of what normal is suppose to be until it gives in and goes back to normal. Much like how 32 metranomes set at different times ends up beating to the same tune.
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