You can edit your own post for the first fifteen minutes after you've posted it. For the first two minutes, you can edit it without the "edited by" message displaying. The time limit is in place for security purposes; people could edit contact info to older posts.
If you need something edited after that time frame (which I think is 10 minutes, though I'm not 100% sure on that), feel free to either report the post using this icon: at the left of every post, or you can post in Ask The Staff and we'd make the edits for you.
