Is it possible for an app to insert an event at a specific date (in the past) in Facebook Timeline?
You can publish an action on behalf of a user at a specific point in time by setting the action's "start_time" property to a date in the past. For more info, see:
https://developers.facebook.com/docs/beta/opengraph/actions
https://developers.facebook.com/docs/beta/opengraph/actions/#timestamps