The 5 minute time limit to edit DMs is far too restrictive, and very arbitrary. If one thinks of something they want to edit, and yet the 5-minute limit has passed, they'd have to make a new DM, which has a chance at cluttering up the conversation with several extra posts that should have been just one. Conversely, I see no reason to prohibit ppl from adding attachments to DMs, as they can be very useful in illustrating their points, and they can serve as evidence when someone is making an argument.