I now have the answers...
1) Each posting goes through a quarantine process by Ariba. During this quarantine, the Ariba Quarantine Team reviews the posting content, commodities, and territories, to ensure that the posting contains enough information for suppliers to respond effectively.
2) The turnaround time for postings to be published is 12 hours. If any changes are required your posting, an Ariba representative will send an email to you requesting that you revise your posting with recommended content. The statuses can be approved or rejected (or revision requested)
3) The posting can be flagged quarantined due to incompleteness, lack of content, need of clarification, etc, a member of the Discovery team will reach out by email directly to the individual at the buying organization who created the posting.
4) Postings by good users are waived from the quarantine process. A good user is a user who consistently provides the required information for each posting they create.