As a Certified Training Professional (Texas A & M)
Department of Education Administration and Human Resource Development - Texas A&M University » Training and Development we are taught that short sessions with frequent breaks are more effective than long session with few breaks.
Two one and a half hour (1.5 ) session followed with a 20 minute break occupy a morning session very well. My afternoon sessions would normally include group discussion and problem solving exercises based upon what was taught in the morning sessions. No, it did not involve music training. And after lunch I did not turn out the lights and show a video. LOL
An hour and a half seems be a good time limit. Frequent breaks and group interaction (if available) are also recommended. Short sessions as outlined above could be used in a two to three day seminar. So if you must practice for extended periods........................ Short session with frequent breaks is the best way to go.