View post time delay based on user group

[mtrac]

I would like to introduce a delay, perhaps 12 hours, before posts are visible by most members and all guests. Until that time, all they would see in the post is a message that the text will be visible at x time. I need to control this by usergroup and user agent, the latter for robots.

Thanks.

P.S.: Just realized that the poster needs to see their post, at least during the time they can edit it.