This MB is moderated. It's not like Facebook where your postings immediately appear. They are reviewed and, if approved, will appear on the MB. How soon your posting will appear depends upon when the moderator reviews submissions. If you post on the weekends, your post might not appear until the following Monday, and there were a couples of periods last year where the MB went for three or four days without an update.
This MB requires patience, but unless you've submitted something offensive or in violation of MB policy/rules, your post will show up eventually.
I know everything, and I'm always right (just ask my husband).