[MileHi]

Laborers in Andrew Carnegie’s mills worked twelve hour days, seven days a week.

Six days

[Leaning Right]

I believe it was six days a week until the Homestead strike was broken. Then Carnegie upped it to seven days a week. A few details are here:

https://www.reference.com/business-finance/did-andrew-carnegie-treat-his-workers-de36d945a374a10f