"Next day homework is not done in our house if it clashes with an activity. End of."
As I said above, next day homework is ONLY set for the first term of Y7, to get them into good homework habits. They are, during that period, always of a sensible length to do overnight - write a paragraph, read a chapter, learn 10 words, do 10 maths problems, that sort of thing. They become longer from the second term of Y7 onwards, in for the next lesson in that subject so usually a few days.
The great thing about DC's school is that the homework timetable is absolutely rigidly adhered to, so there is never 'surprise' homework.
For DD in particular, if we had adhered to 'next day homework isn't going to be done if it clashes with an activity', she would have done no homework at all in the first year of Y7, as she danced every night. Later in Y7 she added school sports fixtures as well ... we narrowly avoided county selection, thank goodness. However, caught between the devil - a school, and parents, who expected a reasonable amount of homework to be set, and a reasonable amount to be done - and the deep blue sea - a serious dance teacher who takes an extremely dim view of missed lessons (and has a string of 3A* at A-level type ex-students to demonstrate that you CAN balance a busy dance life and good academics), DD has developed extraordinarily good prioritisation and time management skills. Tbh, it is that transferable and extremely valuable life skill that will probably be the best and most lasting legacy of her dance years, along with a streak of stubborn perfectionism and a belief in hard work.
Faced with a poster in for the next day, DD would probably do the thinking / planning either at lunch / break (homework club / library) or while walking home, the initial writing in a concentrated burst between coming in from school and her first dance lesson, and the 'decorative' parts either in the dance school changing rooms between lessons, or at the very end of the day / early next morning when not up for 'thinking' but quite able to colour.
Yes, you can say 'she's still a child' and 'she needs downtime' - and yes, she hibernates on Sundays and during the non dance competition holidays. But the lessons in self-discipline, organisation, and responsibility that all this is teaching her go WAY beyond the learning from the content of the homework.
i do think that secondary homework is generally different in nature from primary homework. In a typical primary lesson, there is usually a plan that goes 'Teacher teaches new skill, class practises it together, children do a task that practises that skill more independently, lesson ends'. Any homework is 'additional practice' and tbh is often 'makework' as a result.
In secondary, my observation is that more of the lesson is taken up with 'teacher teaches new skill / imparts knowledge, followed by a small amount of practice'. The independent practice that embeds that skill fully is in the homework, and without that, much of the curriculum is only superficially covered.