In South Carolina, there is no state-specific law that limits the number of hours an adult employee can work straight in a single day or week.
It is not legal in the US per OSHA regulations for an employer to work an employee 8 hours without a scheduled break. In fact, the OSHA rules are to be posted in every break room.
However, labeling an employee as part-time does not change the application of FLSA requirements. The IRS, meanwhile, considers a part-time employee to be someone who works less than 30 hours per week or less than 130 hours per month.
Briefly explain the reason for the overtime request so they understand the context. Acknowledge that it may require flexibility on your part and express willingness to discuss scheduling. Close politely and offer to discuss further if needed. The tone should be respectful, appreciative, and flexible.