Unfortunately, only Android has the widget feature which will show you home/work commute time graph throughout the day. Not sure if iOS will ever get that.
In the future, this kind of feature may be available. It does take a lot of data to mine and present cohesively to the user. It also would need to be expanded to any destination. Pretty limited right now.
The basics are behind the scenes already. A new livemap will have a feature similar to what you are asking. It doesn't allow you to see directly the best (fastest) travel time throughout the day, but it's similar and does show that the data is there.
I also think this is a valid feature request, and one which Waze is probably quietly preparing to figure out how to mock up and develop.