The DOT rule requires airlines to offer a free 24 hour hold or free cancellation within 24 hours of purchase for flights booked 7 days in advance. You could have checked airline web sites; the information is readily available. B6 and UA do the minimum legally required. AA and DL allow it for bookings made 48 hours in advance. AS allows it for bookings made 24 hours in advance.
Citizenship is irrelevant to any of this.