In the course material Master Lin identifies the 5-7 time periods (am and pm) as optimum for doing the active exercises. He identifies the 11-1 time periods as optimum for doing siting meditations (for the reasons Jetay has offered).
One time period is best for clearing blockages (5-7) and the other is best for building your capacity for qi to flow (11-1).
You are perfection.
Iam2 
