The point to the time-limit for edits is not to prevent somebody from changing what they commented after five minutes as an end in itself.
Rather, the point of the time limit is to guarantee some integrity of a conversation in comments without having revision-histories for comments.
As long as there is no conversation this is a non-issue. Of course, deletions can still mess up the flow a conversation. But, this is a different type of concern than a comment that received a reply changing to something else entirely without anybody being able to reconstruct this happened.
Finally, there are some proposals to base the time-limit for editing on the existence of replies, and abstractly this makes some sense. But they are seen as too little of an improvement to bother.
To understand what I mean imagine this:
Comment by User A: You have no idea what you are talking about. This answer is a complete mess. Better read a book on the subject before you answer here.
Comment by User B: Please do not leave such rude and non-constructive comments. I believe the answer is correct.
In this conversation, User A looks bad, and User B reasonable.
Now imagine User A changes the comment to:
- There seems to be an error in the basic definition in the second paragraph, and the formatting makes this answer hard to read. You might want to consult "Introduction to This Cool Subject" for the correct definition.
There is nothing wrong with User A making this change, actually it is very desirable this change happens. Only if it is made by an edit then suddenly the reply of User B looks bad, and this should be prevented by the time-limit. This is less of a problem with deletions, as the mixed-up conversation is a red-flag and if needed as deleted comments remain visible to moderators things can be sorted out.