This is terribly wrong. Everything the Finder displays should be correct all the time. If, for some technical reason, it doesn’t know the size of something and needs to wait, it should show a spinner or some other indicator that you, the user, need to wait to get the information. The actual file size of a folder is what you want to see, and ideally you should see it as soon as you ask for it. — What You See in the Finder Should Always Be Correct