I agree that this time count implementation would only be a competition of who has less of a life. Which may partly be why I don't want this, haha.
Still, though, I just think that if it's going to have its use, it'll only be a "fun" use. Perhaps some people WILL compete for who has the "least life," but I really don't think it'll prove that some people are more active.
As far as comparing it to post counts, don't. If you post in Forums Games, you can get one thousand posts in a week with only a few hours in your bio. If you post elsewhere, one thousand posts will be harder to obtain and will take more than a few hours to achieve. So a person with 500 posts could potentially be more active (time-wise) than a person with 5000 posts.
Still, as I said earlier, I don't think a time count will prove anyone to be either more or less active than they really are. I think that the "last logged on" feature that's currently in our bios should be enough, considering that someone truly is a concern (like some of the Super Mods you brought up).
Avatar: In memory of ieatwyverns <3
Thank you, Vasco <3