Create a new User Group under the Registered one (you can call it TrackTime customers).

Create a new Access Level (you can call it TrackTime customers, too) and add the group you have just created.

Under TrackTime component options, choose the Permission tab. Under the Access Level you just created, grant the browse permission.

Now create a new user for your customer (if there isn't one, yet) and add him to the group you created. Then inside TrackTime customer view, link the customer to the Joomla user filling the field Joomla user.

Finally, create a new Activitiy list menu entry. In the options, set it visibile to TrackTime customers only (the access level we created few moment ago, remember?) and flag the option Customer view.