The problem with that is that the majority of people who join AB probably wouldn't bother to post at all if they had to wait a day. Many of the questions in the 'serious' parts of AB require prompt answers. ('e.g. "How do I help my son with his homework?" or "What's the best way to get from Waterloo Station to Hendon tomorrow morning?").
Of course it would be possible to prevent people from posting in Chatterbank until they'd been a member for a certain period of time, but that would probably only result in the 'idiots' posting in the 'serious' sections, thus deterring genuine new users from posting questions in those sections.
The present system of having a dedicated weekend editor (and an alert team of voluntary moderators) is imperfect but it seems to have improved things a lot since the 'bad old days'.
Chris