1. I'm not sure about the 2 hours, I've always thought it was 1 hour, but can't find anything official in the FAQ. Assume 1 hour to be on the safe side.
2. Editing your post (within that time limit) can delete all the content, but the empty post will still remain. If this bothers you, type an obscene word in the post, when you save it Robomod will delete it and send you a reprimand. As far as I know there are no consequences if you do this, I've done it a number of times.