The rich have begun to work longer hours than the poor

Figures from the American Time Use Survey, released last year, show that Americans with a bachelor’s degree or above work two hours more each day than those without a high-school diploma. Other research shows that the share of college-educated American men regularly working more than 50 hours a week rose from 24% in 1979 to 28% in 2006, but fell for high-school dropouts.

Since the employer doesn't need to offer benefits (the most expensive of which is health insurance) to part-time workers, it's very common to give them 29 or 27 hours per week.

Contrast this with the salaried worker, who is measured by work product, and may work 60 hours per week to justify the salary.