user14697: There's a 5 minute rule about editing comments.
It should be more like 30. Some of us are slow thinkers, need to consult references, need time to review and edit our work, .... 
Buzzzzzzzzzzz your time is up, next contestant please!
If nothing more, check the time the user starts editing, not the time the user save the changes!

user10794: I think it is so that comments don't get completely changed, which makes the subsequent comments (under it) make no sense. Basically if I wait 5 minutes after you make a comment, I can be sure you won't change it.
I think in your case you accidentally pressed Enter half-way through typing a comment, and then had to edit it. In that case you can just self-delete the comment (after copying what you had already typed) and then start a new one, being careful not to do that again.
You have all the time in the world to type a comment, just don't "commit" it half-way through the process.

14697: <p>There's a 5 minute rule about editing comments.</p>

<p>It should be more like 30. Some of us are slow thinkers, need to consult references, need time to review and edit our work, .... </p>

<p>Buzzzzzzzzzzz your time is up, next contestant please!</p>

<p>If nothing more, check the time the user starts editing, not the time the user save the changes!</p>
 10794: <p>I think it is so that comments don't get completely changed, which makes the subsequent comments (under it) make no sense. Basically if I wait 5 minutes after you make a comment, I can be sure you won't change it.</p>

<p>I think in your case you accidentally pressed Enter half-way through typing a comment, and then had to edit it. In that case you can just self-delete the comment (after copying what you had already typed) and then start a new one, being careful not to do that again.</p>

<p>You have all the time in the world to type a comment, just don't "commit" it half-way through the process.</p>
