Total time spent in games
Just like title says - extract the total time spent in game.
Show it daily - weekly and monthly
You're already extracting time from games :)
This can be pulled with the account reporting tool now for the last 4 years worth of replays.
I would recommend that we also show the average total time. I see a comparison of my time blocked vs average time blocked in my league (unranked). It would be nice to see how long games take on average.