http://www.registrar.ucla.edu/calendar/acadcal15.htm shows 10 weeks of instruction in a quarter. There is an extra week at the end for final examinations, and three extra days at the beginning for administrative stuff.
Presumably, that may be part of why semesters are more popular among colleges and universities – there is one fewer set of “overhead” weeks for administrative stuff and final examinations.
My daughter was a full IB student and she belonged to a club team that practiced 7 days a week, 2-3 hours a day. It was difficult but can be done. IB is demanding with the amount of work that you need to do. She definitely learned time management. She went to a top LAC and participated in a Div 3 sport. The first year was fine, by the second year she felt she needed to concentrate on school which was always her priority. She also had a part time job. She dropped her sport. The LAC was definitely more challenging than HS IB if she wanted to maintain a high GPA which was important to her.
I just met a student from our high school that came back home from his freshman year at Tufts. He is a science major and he is involved with music and also a member of a sports team. I am not sure what division that sport is and what kind of time commitment it is though. I asked him the same question posted here and he said he found college more manageable than high school and he did not feel overwhelmed at all. He did very well. By the way our high school is an average urban high school. Not a pressure cooker. Nevertheless he said in high school the busy work was at times unreal and for him to do both orchestra (plus privates etc) and his sport (fall and spring season plus winter conditioning) was a killer. On top of all that he had to practice for the SAT and do million other things. He found his college experience more focused and more enjoyable. I heard the same story for my friend’s D that went to Skidmore but you might not consider this school a top lac. In general I hear this a lot that kids find their college experience more focused and more enjoyable. But this not a real study just anecdotes by talking to my friends kids.