We're testing time limited comment editing again. Had this feature more most of a couple of years then lost it for a while with the site upgrade last fall.
For those curious about why we'd want to limit editing time on comments, it's basically this: frequent editing long after posting tends to result in threads that become incoherent because people have posted in response to stuff that isn't there anymore.
At the moment the limit is set to 20 minutes, though I think we'll probably go up to more like 30 or more. It may be effective enough even at a few hours.