I'm an afterscool nanny and your question should be, "what doesn't the nanny do while the children are at school" I work from 2.30-6.30 and this is a rough guide to my week.
Monday: children's laundry: strip and wash bedding also do one 1 load of darks - hang out to dry and also remake beds and replace mountain of toys! Go round room and pick up nits after weekend of carnage. Feed guinea pigs. Collect from school, other charge walks home by self. Give snack, do homework (normally 1 hour min) and supervise music practice. Give tea (always cooked from scratch - chips once a month as only non made from scratch food), clean up tea dishes, clean all sides with dettol, load dishwasher, sweep floor.
Tuesday: fold laundry which is now dry place in airing cupboard, stick on load of pastels to be washed then hang to dry. Batch cook something for freezer. Feed guinea pigs. Collect 1 from school then drive to collect other from school and drop her and friend at friends house. Give youngest snack, do homework and supervise music practice. Give tea, clean up tea dishes, clean all sides with dettol, load dishwasher, sweep floor.
Wednesday: put laundry that has dried into airer, clothes that went into airer on Tue now ironed and (bedding also ironed obviously). Put laundry away and sort out clothes drawers so that all tops, jumpers, jeans etc and together and folded neatly. Anything with holes/rips/tears taken out and fixed. Bake something yummy. Get any groceries in that are needed (usually the essentials) Collect one from school walking, the other form school in car. Feed Gpigs and give children snack. Give tea, clean up tea dishes, clean all sides with dettol, load dishwasher, sweep floor.
Thursday: Iron clothes that went in airer on Wed and put away. Collect youngest from school take to activity. Come home help eldest with homework, and do last load of laundry. Go back to get eldest from activity bring home. Badger both to get ready for another activity that requires uniform, feed Gpigs, Give tea (from freezer), polish school shoes, clean up tea dishes, clean all sides with dettol, load dishwasher, sweep floor, drop to final activity.
All this is interspersed with resolving arguments, listening to school gossip (ie, someone in school said this today), talking tired children down from tantrums, ensuring they both come home with the right bits, keeping parents happy, pulling curtains and putting lights on when go out, answering door to frinds/neighbours, not letting children go to friends, telling people of for being late and finally having a bit of fun!
Does that help? Would it not work if you found someone who worked similar hours for you as the ones I outlined?