Every so often, someone asks for it, and is denied.
The reason given is that, the longer the edit window, the greater the possibility for confusion when someone quotes or refers to something that no longer exists thanks to an edit.
From this thread :
It’s not just trollery. I’ve seen threads on other message boards fall apart into complete nonsense because of the thread-starter editing the OP to “clarify” it every so often, leading to all of the posts before any given clarification referring to things that weren’t there. No ill will was intended, but it still ended up as a mess.
Exactly. It’s hard to have a conversation when what was said previously can change. There’s also the problem of people quoting text that ends up being changed subsequently.
The five-minute edit window was selected to try to give a balance between allowing people some time to fix mistakes in their post, while also giving the conversation some permanence. The longer an edit window that’s allowed, the greater the possibility for confusion.
But when all is said and done, it’s only a message board post. Typos shouldn’t be a big deal unless they radically change the meaning of a post. And even if they are, and you miss the edit window, you can post a clarification subsequently.