Have you ever posted something, and then realized that you meant to select "My friends" but failed to do so? There is now a 30-second grace period where you can change the message to FO. Just click on the message, select "Change Message Visibility" from the Edit dropdown menu, and click the button.

Why the grace period? Let's just say that experience has shown that some users in the past have shown a pattern of posting personal attacks, then self-deleting them after a couple minutes to avoid moderator wrath. They just hoped the person they were attacking saw it by then.

Anyway, I may extend the grace period in the future, depending on how this goes.