Don’t get me wrong, the script is good, but it only enables the user to know his words and not the ones he’s reading or trying to reply to, like you stated.
I understand what you meant, unlike how OP put it.
You want the post length to be at the footer of every post, whether yours or others, whether quoted or not. By this, it will be helpful to the campaign managers.
Meanwhile, I do not need the information of how long my post should take to be read, it is the reader who needs the information. So, the implementation should be the other way round.
I also do not think that managers follow the post length rule strictly, if they do, we are all going to be behaving like a robot that is programmed to make an x number of posts consistently.
Meanwhile, OP you have done a good job.