I would like to know if there are any restrictions or labor laws for live-in housekeepers. How many days per week and how many hours per day they should work?

Here's a quote from the link below, which (the quote) addresses your question:

A HISTORY OF NEGLECT

While the last century saw important gains for labor rights, domestic workers have been left out of federal labor legislation, including the National Labor Relations Act, the Fair Labor Standards Act, the Occupational Safety and Health Act and various civil rights laws. “Domestic workers lack protection under the law and we have been actively ignored in labor laws since the days of slavery,” said Beatrice, a New York City nanny who preferred to not provide her last name. “Our situation is a critical one since no law defines our rights as workers.”

Source: Domestic Workers United :: Domestic Workers Demand Fair Labor Laws