Unfortunately I think I have the exact opposite problem (don't talk enough) but awesome work! And thank you for making and clarifying that it is private and 100% on device. More tools need to be like this!
I have had this on my radar as well and, in a way, you can totally use it to track your non-speaking as well.
Here's an idea: What if there was a toggle for your scenario and the count-down of "other people talking" started when you're silent.
The colors on timeline would be inverted, you'd see your "airtime" as a few gray dots.
What do you think? Would this be helpful?