Graphing when your Facebook friends are awake
You used to be able to do this with the Facebook Query Language (FQL) that Facebook exposed, sending something like this query to the FQL endpoint.   SELECT uid, name, online_presence
   FROM user
   WHERE online_presence IN ('active', 'idle')
   AND uid IN (
     SELECT uid2 FROM friend WHERE uid1 = me()
   )

Unfortunately, the current version of the Facebook Graph API[0] doesn't have the online_presence field, so this is no longer possible. Maybe the Graph API will be updated in the future to also return the online_presence fields?[0] https://developers.facebook.com/docs/graph-api/reference/v2....