Thank you for the information and your question. Although Oregon does have a law that restricts the number of hours a week a nurse can be forced to work, the law only applies to hospitals. This is the link to the law: http://arcweb.sos.state.or.us/pages/rules/oars_300/oar_333/333_510.html
Otherwise, Oregon does not regulate the maximum number of days or hours a week an adult can be forced to work.
As for the leave issue, employers are not required to offer any paid leave. If they choose to, they set the rules for the use of that leave. As long as they aren't targeting one particular employee for worse treatment simply because of the employee's race, national origin, sex, age (over 40), disability, religion, pregnancy, military service, or AIDS/hiv status, they can set the rules they deem appropriate.
That said, if his mother has a serious health condition, he may qualify for intermittent FMLA that would give him the right to take time off without having it effect his attendance or job. This is available if the employer has at least 50 employees and can be used or up to 12 weeks aggregate time in a 12 month period. He should speak to HR about that.
Please let me know if you need any clarification.