Project managers are usually expected to answer their phone until around 7 PM, but they are not on call. They usually work a minimum of 50 hours per week. There are designated on call technicians that work nights and weekends.
On call one week every two months.
Everyone is on call. I work vastly changing hours from project to project.
The first responder is normally the mitigation technician. However, project managers should always be available to their techs.