You do not have to wait for 24 hours before the post is deleted. Just edit it to delete and report it to moderator. I noticed moderators are deleting it before 24 hours. Even if not deleted by a moderator before 24 hours, moderator will still delete it for you so that if you do no remember, it will still be deleted.
It is possible but I would not mind to bother moderators with my report. If I apply in a signature campaign, and later change my mind within 24 hours, I will do things by myself: either editing it to "Delete" or "Withdraw my application" or use Strikethrough. After 24 hours, I will return and delete my post, and this way I don't create more task on forum moderators.