If you would like Approvers access to time tracking, you can enable this within their User Permissions. 

Within - People - Users - select the action button against the relevant employee. 

There are various individual permissions you can allow against the approver. 

For access to time tracking, tick the box for  - Allow approver to access time tracking?

Select Submit to save these changes. 

When the approver logs in, they will have access to Time Tracking records for individuals which they are set as an Approver for.