In my opinion, in response to some queries,
Quality means sincerity and focus. Quantity means actual time spent or repetitions made, but without injury.
Quantity Guideline 1: Average Quality student should practice 20 times of Highest Quality student. And, Lowest Quality student should practice 100 times of Highest Quality student.
Quantity Guideline 2: Yoga Teacher Trainee should spend 20 times more time than average Quality Student.
Quantity Guideline 3: For one simple exercise, an average Quality student should should spend at least total 1 hour of practice. For medium level exercise, at least total 20 hours of practice. And, for difficult exercises, at least 100 hours of practice. This guideline is for a Yoga Student. For Yoga Teacher Trainee, see the Guideline 2.
Note: all the timings given in hours are total spread over maximum period possible.