"It should only take 30 minutes per night Mrs Doodlez".
"Stop after 30 minutes and just write a note in the homework diary Mrs Doodlez".
IT.
DOESN'T.
TAKE.
JUST.
30.
FECKIN'.
MINUTES.
He won't stop after 30 minutes. It HAS to be finished. He gets upset and frustrated and tries to swear blind that if it's not finished, he'll be sent to Broadmoor detention.
He won't accept that's not the case.
He's 8 years old.
An 8 year old should not have to give a toss about homework.

[as you were]