After how many hours per day/week are retail businesses required to pay health insurance for employees?

Need the answer for a story I'm writing - thanks in advance
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Businesses are not required to pay health insurance for employees.Some businesses offer the insurance but they are not required to.Company paid insurance is just an added benefit for employees and some companies pay the full amount while others require you to pay the full amount. I work in the medical field and even my employer requires us to pay the full premium which is a few hundred dollars every 2 weeks and i pay even more to add the family.
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