In Sage HR, click your name in the top right, then click Settings.
On the settings menu click Timesheets,
On the "Employees with timesheets" group, click Eligibility.
Select the employee(s) you want to assign to this group. You can search for them by name or use the advanced search to filter down to employees of a certain Position.
Once you add an employee to a timesheet group, the Timesheet option appears in their main menu on Sage HR.