Estimate total daily homework time by subject.
Homework planning fails because it counts work and forgets breaks. Four subjects at thirty minutes is two hours of work but, with a ten-minute break each hour, twenty minutes more at the desk — which is the difference between finishing before or after a bedtime. Breaks scale with work time rather than being a fixed block, since that is how attention actually behaves. The weekly total is what to compare against guideline homework loads for the year group.
Work and breaks
Work minutes = subjects x minutes each; break minutes = work hours x break per hour
Elapsed
Time at the desk = work minutes + break minutes; weekly = elapsed x homework nights
A widely used guideline is about ten minutes per school year level per night, so roughly 60 minutes in year six and 100 in year ten. Consistently exceeding that is worth raising with the school.
Interleaving different subjects improves retention but costs a few minutes of restart each switch. With four subjects that is real time, so batch each subject rather than cycling between them repeatedly.