There are a LOT of variables in that equation.
The diagnosis (if there is one)
The accuracy of the diagnosis (what is the true underlying cause)
The layers of disease that form due to length of time from onset
The accuracy of the frequency program (CAFL is general at best)
What lifestyle, environmental or other causes continue to influence the individual.
My personal opinion is that if you are able in some way to determine that you are choosing the correct frequencies to run and/or if the person is employing other holistic procedures to minimize offset to the results, then somewhere between one week to a month should let you know if *something* is happening.
A Doctor who treated people with Stage IV cancer used a lot of different therapies (diet was essential) and could produce amazing results in a six week time period. Months of follow up could be required for the body to repair itself and for the Immune System to achieve lasting homeostasis.
Wish there was a more definitive answer for you. Some disease conditions are going to require a lot more than just remote treatment if you want to see results in less than months.
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