Is there a way to check how long people have been in a guild?

I was wondering if there was a way to check each member of a guild how much time has passed since they were invited, for guild management purposes.

The game itself doesn't have that information stored but I'm betting an addon exists.

That information would be in the guild log so the game does keep that information but I guess there is no way (originally) to get that info

Correct, but the log has a fixed capacity, same as the guild bank logs. That's why I assume an addon exists to provide a complete log, but it would require you to log in periodically for updates.