[_Microft]

I'm neither a doctor not a psychologist but here is a wild guess: I would assume that it takes about as long to train yourself to work with a BCI as it takes to e.g. learn to reliably wiggle one ear, raise an eyebrow, just any voluntary movement that you do not control yet. Reasoning: in both cases you would have a feedback loop and would need to learn to reliably create the appropriate output and that it does not matter a lot whether the output goes to actual muscles or via EEG to trigger a response.