Right now, for 5 minutes, you're able to edit any comment:
Even after the 5 minute grace period, this edit button still works/is enabled:
The user is mislead to believing they can edit their comment, and spend time improving/updating their comment, only to recieve this message:
For larger comments, this can be quite frustrating. I'd like to recommend some client side checks that when the comment reaches 5 minutes old, the edit button is removed from the client side (Or as soon as they hit the button, if it's more than 5 minutes old, display the error message). Additionally, if the user hits the edit button before the 5 minute period, I recommend a server side grace period (Somewhere between 1-5 more minutes) to allow the user some additional time to finish their edit.
While the duplicate mentions part of what I'm proposing, it does not going into detail about server side grace periods, nor how the edit button should work at 5 minutes (I offer a few different solutions). I find it difficult to justify editing the other post to add my suggestions to that post in order to make it resemble an exact duplicate (As stated in my comment below)