The current window is 5 minutes. After you post, at the bottom left of the post you'll see your username, the time it was posted, an edit link, and a report link. I'm not sure, but maybe it won't display if you load the page after the window expires. EDIT: 25 minutes later can still edit. Will check again in an hour or so. EDIT 2: Over an hour now--should be good to go.