It was the 2nd comment, and since it's not been very long since the first one I remember that I edited it quite extensively, many times, for well over five minutes. This time I could start editing but could not (successfully) submit the edited text just two minutes after posting the comment, according to the time printed just above my comment after I submitted the edit (which only showed the text before the edit, and the "Edit" link was now gone).

Then I don't know. You normally have around one hour to edit, IIRC.