Wow!
App to calculate play time + stats visualizer
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Very cool!
Indeed very cool! 
What I would find very interesting would be a slightly different variant of the heatmap, where instead of absolute values of Wins/Losses I can see my relative chance of winning regarding to that exact timeframe. So I can know at which times of the day I should play, and when it is better to avoid it. 
I've been working on Chess Time for almost 2 years on and off as a way to calculate your play time on Chess.com. I just made a big update on the design and the stats that are available. It's quite nice what you can do with the public API.
Now you can track your nemesis and victim players – it's pretty neat to see those stats in action!
https://www.chesstime.io/
The app was built with React and Typescript. There is no backend yet but I'm looking into the possibility of building one.
Here's a sneak peak:
A nice breakdown of the win/loss/draw conditions
The player that you played the most games with and the player that you have won/lost/drew the most against. As you can see, I love playing against bots.