<p>You have a five minute editing window.  (Same as for editing questions and answers without showing as a new edit.)</p>

<p>There are no limits on deleting your own comments.</p>

<p>I know there should be a better SO.meta post about it, but I did find <a href="http://meta.stackexchange.com/questions/33997/please-ditch-the-five-minute-window-on-comment-editing">http://meta.stackexchange.com/questions/33997/please-ditch-the-five-minute-window-on-comment-editing</a>.</p>