Can you provide more details like, when the schedule job starts at 23:00,
1. Does it fails with any error messages or it goes to queued or any other status in the job monitor but does not fail with any error ?
2. Is the job a single job or is it a policy based job ?
3. If the job is failing with any error, can you tell me what events do you see under application event logs for next two to three hours counting from the time the job is scheduled to run ?
you can also try following
http://support.veritas.com/docs/307609 .