What business value would your suggestion represent for your organization?
Be able to add or correct information in the original post without re-posting that information as a comment.
For a limited time you can edit/correct your post.
After that time, it would be better to add additional comments so that replies would not be taken wrong if someone edited the original or any subsequent posts.
To confirm @Dale_Rosema you can do that for 60 minutes following the publication moment. Indeed we need to preserve the integrity of a conversation / chain of comments.
Sadly, I have had an experience where a post was edited in an effort to make my response look "poor" or to make the original poster look more intelligent or for some other unexpected reason...
I agree that this 60 minutes rule is not very clever and does not preserve the integrity of a conversation as @olivierlp wrote.
It would be much better if a user would be allowed to edit a posting of him as long as nobody has written an answer to his post (to his post, not in the thread elsewhere).
I would also suggest that a user should be able to withdraw a posting (deleting his posting) without having to ask a mod to do so as long as there is no answer to it.