I don't understand the Relevance duration field

I'm not sure how to properly set the relevance duration field. My expectation is that a relevance for a timeline entry would be valid until the next timeline entry takes over, but that doesn't seem to be the case.

Let's say my widget contains info about an upcoming event, and the event is in 2 days. My code calculates a relevance score from 1-100, where 1 is two weeks away and 100 is at the moment the event starts. The goal would be to set the relevance so that it slowly increases as the event gets closer.

How often should I update the timeline entry with a new relevance? And if I update the timeline with a new entry every 4 hours let's say, do I make my relevance duration 4 hours? Or something shorter? Or longer?