Make Service Request not visible to colleague employees

Our Call Center agents maintains their time via Tasks in Service Request i.e when they are working on call, a task is created as 'Working on SR' and record the duration of time spent on that SR.

Once a month each employee creates a 'Internal SR' where they record time spent on non-SR such as meeting, vacation, illness, admin etc as each Task Type.

What we need to achieve is that the 'Internal SR' created by each employee should not be visible to other employees, this is needed to make sure each employee cannot/should not view the time spent by other employee.