That's very hard to say because it depends on how the disease develops. We often cite the example of Alzheimer's disease, which is a gradual deterioration of capacity, but there are other neurocognitive disorders where the deterioration won't be as gradual. It's impossible to predict. It may last many years or only one or two years, as in the case of fast developing dementias.
On October 25th, 2022. See this statement in context.