When is a photo added to photo stream after you enable the service?

When you enable Photo Stream, any new photos you take on your device are automatically uploaded to the service. They are added to your Photo Stream shortly after you capture them, typically within a few moments. However, the exact timing may vary based on your internet connection and the settings you have configured for the service. Existing photos from your library are not automatically added; only new ones taken after enabling Photo Stream will appear.