Depends on the nature of the homework, the interest of the child, whether this is typical for kids in the same classroom or whether it's this long because the kid is unfocused or struggling. Or is this additional homework from parents?
I let my DD10 (5th grade) do an hour of effective math a day, this includes the online math that she does at school. So if she uses the math time at school efficiently, she doesn't need to do any math after school. For her level of interest in math (somewhat interested, very strong math student, but definitely has other stronger interests), I think this is enough.
