There are sectors in Mexico where the curtain never comes down. A Pemex refinery, a glass smelting line, an automotive plant with just-in-time production, a tertiary-level hospital, a data center hosting banking services: they all share something. They operate 168 hours a week, 365 days a year, without pause. When the reform arrives to move the workweek from 48 to 40 hours, these operations are the ones facing the thorniest problem in the country. It is not an opinion; it is hard arithmetic. Here I break down the case, with a staffing calculation that most reports gloss over.