Inventory changes are stored in the History table and will not be show in the normal inventory view. You will have to use SQL to produce anything of substance. Logon History is stored initially in the registry:
The issues I see in what you are trying to accomplish is that you must have the inventory scanner set to run at logon, and then a scheduled task to run at logoff. Depending on your environment, and user habits, that may produce a substantial amount of data. Why are you trying to capture logon and logoff times? The only "true" way to accomplish this is to to use security event logs.
Thanks for the info. Actually, I think the info here will help me HKLM\Software\landesk\inventory\logonhistory\logons. I wonder what the string values are associated with? it doesnt look lke a time number. (1293653121) I bet it's just a database ID somewhere? hmmmm.