The fields that could use are the Last Basic Inventory field or Last Configuration Request.
The Last Basic Inventory field comes from the Inv_AeX_AC_Identification table
The Last Configuration Request field comes from the Evt_NS_Client_Config_Request table.
These tables can be viewed from Resource Manager.
Out of the box the Symantec Management Agent on client sends a Basic Inventory to the Altiris Server every 24 Hours and the Last configuration Request check defaults to either every two hours or 4 hours out of the box.
You could use put the following sql query in a custom Altiris sql report to get this information
select
c.name as Computer
,c.[OS Name]
,c.[User]
,bi.[Client Date] as [Last Basic Inventory]
,ccr.[Config Request]
from vcomputer c
left join Inv_AeX_AC_Identification bi on bi._ResourceGuid = c.guid
left join ( select resourceguid, max(_eventtime) as [Config Request]
from Evt_NS_Client_Config_Request group by resourceguid
) ccr on ccr.ResourceGuid = c.Guid
order by ccr.[Config Request]