An hour maybe two for my ds(6). He's year1.
The school sent home a massive work pack that is supposed to last four weeks, it works out as a bit of reading and writing, one double sided maths worksheet, one double sided phonics worksheet and then a bit of 'other subjects' - art, geography, history, science etc.
A lot of the 'other subjects' stuff is things that we teach dc anyway by sort of osmosis because he's still pretty curious. So he'll come out with a random question like 'why are crows black?' and we'll fall down the Google rabbit hole, and we'll discover the actual reason why (twilight hunters so black is the best camouflage) and also the reason that other cultures came up with like the African tale of how the crow turned black (use to be colourful like parrot but flew into the sun and burned black, been black ever since.)
He's into pokemon so will use that as a seuge into world religions (lots of pokemon are based on Japanese kami so watched a few videos on YouTube on shinto).
He's got a crafty corner and I'll set him a challenge like build a bridge that this toy car can drive over and I'll call that a science lesson (physics, engineering).
We play shops and that's maths working out prices and change.
It's all very relaxed here with only a vague timetable of breakfast, a few work sheets and a bit of reading then lunch, then we potter around until it's time to make dinner.
Sometimes the pottering around will be ds playing on a tablet doing phonics or maths games, or watching cartoons. He'll play in his room, help me in the garden, help me clean the house etc (he likes dusting and hoovering, who am I to stop him
)
Six hours is ridiculous though. I don't believe that for a second. I reckon the average for primary kids is 1-2.