Each lesson is approximately 15 minutes in duration, although you can finish sooner. 

• Research shows that spaced repetition is the most effective study strategy for developing neuro-muscular skills (e.g. practicing a musical instrument).
• NativeAccent studies show that 30 active learning minutes a day x 5 days per week produces the optimal balance between study time and competing student priorities.  
• Studying 2 1/2 hours at one sitting has shown to not be effective.

Related Article: What is Active Learning Time and how is it calculated?