Google Maps recommended "leave at" time: how reliable is this?

Google Maps provides a feature to estimate your arrival time based on typical traffic along your route. It provides this time as a range, e.g., "typically 1h - 1h 50m" Based on that, if you select to arrive at a specific time (vs. leave now or depart at), it will tell you what time to leave given the high end of the range. My question is: if you follow the advice and leave yourself the high end of the estimated travel time range (1h 50m in my example above), how likely are you to arrive at your destination on time? This is a rewording of this closed question: How is the range of Google Maps new drive time feature defined?

I fear it is not the same all over the world. It also will depend a lot on things like weather and local reactions to it.

How is this question different than the original (you yourself said it's only a rewording)? If it isn't and it's the same as the one closed as off-topic, I think this one should be closed too.

Difference in question: the original question was asking about their approach for determining the interval; I'm asking about how I should use the information as a driver.

I am asking in context of US. What my question gets down to is, how much variability is already accounted for in the range Google provides, and how much additional margin of safety do you need to add to that range?