If it's opinions you want, I have them.
I think it is unreasonable to require 3 hours of work on Saturday. I also think, that paying your children to do things to help the family is unreasonable. Children should have chores that they do without money rewards because it's part of being a family. Everyone has chores. To me, allowance is money that a child recieves irregardless of chores.
That said. I don't think doing 3 hours of work a week for a teen is unreasonable at all. The part I think is unreasonable is that you require them to do it on a Saturday. Why not let them spread these chores around their own schedule instead of yours? They can set up their own convenient times to do them. Maybe one hour Saturday, one Sunday, one Monday etc. I think they'd be much more willing to help (ok maybe not willing but would complain less

)if the times for the chores were times they could choose themselves. It would probably help to have the chores listed in some way so that the kids could add the day that each chore would be completed by.
Good luck to you. It's a bummer listening to them complain for sure.