Wow, Joannek your helper is very hardworking ! From memory you are the one with the mother-in-law who expects a 10 course lunch?
I think that different families and to a certain extent different cultures have different expectations. Also, I only work part time so that makes a difference.
3 days a week (usually Mon, Tues, Wed) our helper works from when I leave home (around 7am) to when I return home (6pm). She generally has dinner ready by 6pm and I feed the children/bath/bed/etc. My husband and I heat up the dinner later for ourselves. We have a dishwasher, so it is no trouble to put the dishes away and turn it on.
She also works one extra half day (Friday morning) to catch up on the cleaning that she can't do when I'm at work and she is looking after the girls.
She will also 'babysit' from time to time if my husband and I go out to dinner. We usually leave after the children are in bed.
So, she works 3 long days and one short day. And yes, we pay her a fulltime wage.
We always get up to our girls in the morning, we always get up to them at night. Our helper has never done this, never will, don't want her to. When I'm home, I like to have 'family time' without a helper. I enjoy playing with my children, cooking for them and looking after them. My children are my privilege, not my work. I don't always enjoy picking up their mess, but I do it.
I am not judging people whose helpers work longer hours, you have to do what works for you and your family. My personal view is that the helper is working and the hours should not be longer than I would work in my job, wherever possible. They are people too and need time to read/watch tv/chat to their friends/rest.
I don't understand people who let their helpers get up to their children in the night and first thing in the morning. You are the parents ! OK, sorry maybe I am judging, can't help myself.
But the OP asked for the legal hours - I have no idea. So far as I know it is an agreement between the employer and helper?????