My DW spent some of her childhood outside the US as well, and she's also critical of the amount of time US kids spend in school... especially when you break it down and find so much of the time wasted by waiting on other kids to finish work, lining up, etc. I tend to agree with her.
We encourage our DD to finish as much homework as she can when time allows during school. So if, say, she does a math exercise in class, and finishes early, she could get started on the homework assignment.
Otherwise, any organized activities DD is involved in tend to be finished by 6:30pm, immediately followed by dinner and homework/study, as necessary. If she doesn't have an activity, that period between school and dinnertime is hers for unstructured play, usually with friends.
