Holy hell, I was just lamenting Google Maps' lack of such a feature, and the range of commute time estimates being way too conservative. Lo and behold, they had the feature, it was just in Waze.

Thanks, that's a nice feature that makes it worth having on my phone. I'll still switch to google maps for the actual navigation because of the cleaner UI, but being able to look this up ahead of time is useful.

How can I access this graph in Waze?

By choosing "later" instead of "go now" after picking a destination.