The design of the forum is set by the program (xenforo) and the edit time is set up by the owner. Each editing window was created by him so feel free to drop him a line at
@JmpMster but I'm 99% sure this is at the bottom of his list of life decisions at the moment. He doesn't choose to tinker with any of this these days and the editing remains as is because what is posted is a pain in the ass to edit for ME later. Look at it this way - you write something and the next person replies. You edit that post but now the initial post has been quoted so now you want THAT post edited also because it says what was initially written. Or, you write something and the next people start to reply. You realize what you wrote was shitty / racist / wrong / needy / against the rules / fill in the blank with literally anything here so you edit it. Now all the responses following yours look "off".
I do realize that not having a uniform time of editing is odd. *I* don't even know what the windows of time are. I just make sure what I'm posting is what I want to write. Some of them are 5 minutes, some are 10 (I think this was a fluke in software switch). Some forums have an unlimited time to edit and others have zero. I realize it's a bit unnerving.. I have also found it to be at times.