I'm afraid this is directly not possible. There is no database field - to my knowledge at least - that would contain a static entry regarding agent installation date.
You can however do some tricks that might serve this information for you, such as setting the ASCI a large value so the Last Update field holds the first ASCI value long enough to make reports. (The first contact always occurs within 10 minutes filling the Last Update field, then the agent policy is downloaded setting the ASCI a large value on the client so the first contact value is preserved for some time in this field)
You can use the Last Update field value to fill the CustomField field for the clients and later you query this field for agent initial installation date.
this is wrong - there is a database field; please try this statement:
select top 100 ln.nodename as 'Name', ln.NodeCreatedDate , cp.IPAddress , cp.domainname ,AH.ComputerNAME as 'AgentHandler' from epoleafnode as ln, epocomputerproperties as cp, EPOAGENTHANDLERS as AH where cp.parentid=ln.autoid and ln.nodename like '*%*' and ln.lastupdate<>'' and ah.autoid=cp.LastAgentHandler order by ln.NodeCreatedDate desc
the field NodeCreatedDate isn't available in ePO - but why?
Thanks. I've also considered using the NodeCreatedDate, but unfortunately, this records the date the device first showed up in ePO, regardless of whether it is managed or unmanaged. Since we are using AD sync, the devices will show up as unmanaged for some time before the migration is performed and they become "Managed".