In Timesheet Billing report,supervisor cannot be restricted to view data only for the users who is reporting to him. When a user who has supervisor permissions runs Timesheet Billing report,either no data will be displayed for him or the report can include data submitted by all users against the selected projects If the Supervisor's permission includes the 'Can View All Report Data' option and hierarchy filtering is not enabled.

This is because Timesheet Billing report is meant for the users who has Project Leader permissions or, if their permissions include the View option for All Projects, they can view data related to all projects or If the user’s permission includes the Can View All Report Data option and hierarchy filtering is not enabled, the report can include data submitted by all users against the selected projects.