The customer is looking for a report that shows the date and time that the computers last checked into the ITMS system.
In the Symantec Management Console go to: Reports>All Reports>Notification Server Management>Agent>Agent Connection Status.
You will see the following:
The last column in yellow above (Reported) indicates the last date/time that the agent checked in.
In orange above, you can Save the report as a spreadsheet and manipulate it the way you want.