Yeah, it'll just lead to a change in proofreading habits. That isn't that big of an issue tbh (apart from those of us that sometimes make early morning postings before having had their first cup of coffee!), but there are more practical complications, such as wanting to swap out one picture for a more refined one, or adding additional links, fixing a quote or img tag, or simply adding an extra paragraph or PS. It could of course be done by simply writing up another post, but it is far less practical, and it'll be a little weird when one is posting a reply directly after their own post made half an hour ago when they're only adding a sentence or two of additional content.
I just feel like having a time limit on editing is an unnecessary complication, and it's definitely the first time I've come across such a function among the boards I partake in. Or at least make it practically longer, like 24 hours or something.