If you type a comment, and click on the 'edit' button after 5 minutes, it says that "Comments can be edited for only 5 minutes". Why can't the button just disappear after 5 minutes, so we can assume that the comment is non-editable now.
I use the edit function post-five-minutes frequently and certainly hope this feature/behavior is never revoked.
As much as I find the "gotcha" feeling of finding out too late that I've passed the five minute mark even though I'd swear I had a few more seconds, I find the availability of edit without save is still very useful.
Unless I'm mistaken, there is no other way to grab all of the links, formatting, and MathJax at once, to either repost, revise or improve the comment when it is helpful, or to use it as the kernel of an answer when I realize that it was one, since I try to avoid leaving answers as comments as much as possible.