While SocialOomph, Sendible and HootSuite offer the same kind of service, the simplest way to schedule Facebook status updates is by using the easy, free LATER BRO service.
Just sign in with Facebook Connect, select your time zone, type in what it is you'd like to say, set the calendar and clock to when you'd like to say it, and presto!
Just sign in with Facebook Connect, select your time zone, type in what it is you'd like to say, set the calendar and clock to when you'd like to say it, and presto!