I'm not so sure Kaolian, because I can access my post history, and for example as of right now I may become a Sage at some point overnight because a post I made today has been rated up. However, if someone rates a post that I made yesterday or before, then I think it does take effect immediately (or as of my next post). The other possibility is that there is a time delay after a post is made before any ratings to it affect the user's average rating. So here's how I think it works:
User with 3.00 makes first post, someone rates it up shortly thereafter (any amount will affect the average rating), average rating does not change until sometime overnight (or a certain amount of time has passed). User becomes a Scholar, but then someone rates the first/only post down, and the user loses Scholar immediately (or as of next post).
Perhaps you could investigate this phenomenon further, because by your post this may not be how the system should be, and also by me making this post I may be in fact lowering the effect of the eventual increase to my rating.