Legally you need to have 10 hours notice before STARTING short call, that's from the time you acknowledge the assignment to SC. You don't have to acknowledge a SC assignment (or any assignment for that matter) on your first on call day till 0200. Which means scheduling would be stupid to try to schedule you for SC that starts prior to 1200 - there would be no way for them to count on you actually being available at that time. You would have to acknowledge at exactly 0000 to be legal for a 1000 SC start. The 2 hour call out has nothing to do with it.