It happened several times to me that I could not submit an edit which I made on a comment, since the comment grace period was over meanwhile.
I acknowledge the grace period as such and know about the background, but it is a little awkward to be able to edit a comment, fix some mistake, but then not being able to submit it anymore since the grace period has timed out during the edit.
Would it not make more sense to check the comment grace period when starting the edit, and allow submitting an edit in any case?
In order to avoid a potential backdoor where users intentionally start the edit action within the grace period, and then just leave the edit window open to be able to edit and submit a comment even after a very long time, it should be sufficient to add a separate "edit timeout" of, for example, 10 minutes. This would still allow to finish quick fixes which have been started shortly before the grace period times out.