I think that message is unclear and should be changed to something like "Comments may only be edited after 5 minutes" or "Comments may only be edited 5 minutes after posting."
In the English language, your suggestion would mean that comments could only be edited, 5 minutes after they were submitted. Which of course is not the case, and in reality, after 5 minutes have passed you no longer can edit a comment.
The statement as it is currently is grammatically correct.