David, you are right...

11-1 at noon and midnight for Sitting Meditations, especially the Small Universe. Master Lin says the front and back energy channels connect during this time period, and therefore you receive more benefit with less effort.

5-7 in the morning and evening for Active Exercise. Various channels are also open during this time period making it best for the Active Exercise.

But hear this warning: the best time is any time you can practice.

Don't put off practicing because it is the between the above mentioned time periods.

30 minutes at 3:00 is better than no exercise at all.