Pigeon eggs?

Does anyone know how long it takes pigeon eggs to hatch, and once they do hatch how long before the babies leave the nest? Some genius who lives in my building opened the windows at the top of our stairwell and a pair of pigeons has come in and right on top of a window have built a nest and they are sitting on eggs. If I had known soon enough I would have torn the nest down before they laid eggs, but now since they have eggs I don't want to be cruel, they been sitting for awhile now and I'm hoping they hatch soon. As soon as the babies are gone I want to get rid of the nest and close up those windows.