To clarify, are you asking if, after 5 days, the image will be refreshed when viewed? Based on your screenshot, no; it would only be refreshed every 10 days.
If an image 404s on an update, the old version will be served until the image "naturally" expires. We will continue occasionally attempting to fetch it until it errors too many times (then we assume a permanent error).
If an image is returned and it uses a 2xx response code, that image will be assumed to be the correct image and the proxy would be updated with it.