I've been trying to figure out how to see game session length stats for my mobile games. I have games on both the iOS store and Google Play store. But on both of the developer consoles I can't find any statistics related to session length. Hoping someone could point me in the right direction.

You could integrate something like Google Analytics for mobile apps. The Game Analytics platform also exists and could provide more information about player activity than a generic mobile app analytics solution.

We used Google Analytics some years ago with great success, but there are many similar platforms. “Analytics” is the key word and then you can throw “games” or “mobile” in there.