1The incubation period for covid-19 can be even something like 14 days. I guess this can be caused by having no specific immunity to this disease, so it takes some time for the immune system to react. And since some of the perceptible symptoms (e.g., fever) are caused by the immune system, the incubation period can be long.
However, if a vaccinated person is infected despite the vaccination (as it is not 100% protection), does the immunity lower the incubation period? How much? I believe it is reasonable to expect it, as the immune system has at least some idea how to react to the specific disease. This would mean getting the fever earlier, but in a milder way. However, I might have missed something or I might have just discovered some factor with minimum impact. I was unable to find if and how much important factor it is.