So the question is, there's a situation where a literal notes appears or it's description how little happened in this time?
1 Answer
You just need to understand that the phrase of note is a fixed expression that means worth paying attention to or, more literally, worth being noticed. Therefore, little of note would mean something that's not really worth paying too much attention to. The following is a paraphrased version of your original sentence:
As time passes, not a whole lot worth paying attention to happens/occurs.