There is no daily overtime. An employer can schedule a part-timer for 12 hours on Tuesday and 4 on Thursday without triggering overtime, provided the weekly total stays under 40.
In the complex landscape of U.S. labor law, the distinction between full-time and part-time work is not merely a matter of hours—it is a threshold that determines eligibility for benefits, overtime pay, and workplace protections. While the Fair Labor Standards Act (FLSA) famously declines to define "part-time" status, the U.S. Department of Labor (DOL) has issued critical guidance over the decades to clarify how employers should classify, pay, and manage part-time workers. dole explanatory bulletin on part-time employment