Hi there, Michelle.
When you grant a Time Tracking Only access to one of your employees, they will have both access to the Weekly Timesheet and Single Time Activity.
If an employee entered the hours under Single Time Activity, they can either Add or Overwrite it from the Weekly Timesheet page.
You can check this article for more information: https://community.intuit.com/articles/1767762
If you have any additional questions or concerns, please reach out to me. Thanks.