The contagious period is from two days to two weeks, if it's bacterial pneumonia, after 48 hours of antibiotics treatment it's considered not contagious any more. If it's viral one, you better consider two weeks. Chemical or fungi are not contagious. For incubation, pneumonia is acute, when the pathogen reaches the lung in half day pneumonia can occur. But it doesn't mean in half day after contacting the pathogen pneumonia occurs. Pathogen starts from respiratory tract and goes down to the lung. Like flu virus, when the virus goes into your body from the nostril, or throat, or eyes, it stays there for several days(incubation), then you have flu symptom, when the disease develop, the virus goes to the lung, pneumonia occurs.