Okay, so it seems like the time limit on editing also applies even after you have pressed the edit button... Meaning if you decide to edit a post, and spend ten minutes writing up a long and detailed reply (because you don't want to post two consecutive replies), your edit will not go through if you click "apply changes" after the time limit.
And there doesn't appear to be a way where you can retrieve what you've written during your edit either...
Typically, you should use notepad or something of that nature when you are formulating a long reply. If you know it will take 10 or 15 minutes then I wouldn't sit there with edit button or reply button writing it up as over the years, I've lost countless amount of text like that so I use notepad/Notepad++ to write long threads/replies.