Is there a reason temporal constraint in editing comment is more important than thoughtfulness, on this site? Better for my plodding mind to be precise than fast, isn't it?
This question is answered on Meta Meta, which is where features common to all SE are discussed. There is nothing special about 5 minutes in particular, but "if you're allowed to edit a comment for much longer than 5 minutes, it becomes possible to perform an edit on the comment that makes it out of context (no longer makes sense) with the rest of the comments", and revision history on comments is not recorded, see Why is the time limit for editing comments only 5 minutes?
This question isn't really about philosophy, it's about the way this website is managed. However, I agree that a 5-minute editing time is too short. I just got cut off halfway through improving the clarity of a comment, so the comment survives in a longwinded, less clear form. I guess the lesson is to write your comment offline.
If the comment requires a lot of thoughts then it's better to draft it elsewhere before posting (Notepad perhaps). If it's not, then the trivial fix can be added by deleting the old comment and posting a new one.
If there is a reason for the time-restriction on editing comments, I don't know what it is. If I take 3 minutes or 30 minutes over a comment, how am I inconveniencing others ? There is no danger of more time meaning excessively long comments, because comments have a strict word limit.