using powershell to find user sessions longer than X duration

I wan to return the session objects longer than 7 days but cant figure out the format of the duration parameter.

Get-RemoteSession -Duration ?

help says:

-Duration [<string>]

     Filter based on the duration of this session. Using the format: 'dd

     day(s) hh hour(s) mm minute(s) ss second(s)'. Zero values will be

     omitted.

Can someone show me an example?  I want to then look up that user in AD, retrieve their email address and send them an smtp email.

Here is what I have so far:

add-pssnapin vm*
$FromAddr="First_Last@domain.com"
$FromName="First Last"
$CCAddr="First_Last@domain.com"
$CCName="First Last"
$SMTPServer="smtp.mailserver.tld"
$VDISessionObjectArray=(Get-RemoteSession -duration >7 days)
foreach ($VDISessionObject in $VDISessionObjectArray)
{
$ADUserObject=get-aduser -filter 'samAccountName -like $(VDISessionObject).Username' -properties mail
$ToAddr=($ADUserObject).mail
$ToName=($ADUserObject).SurName+", "+($ADUserObject).GivenName
send-mailmessage -to "$ToName <$ToAddr>" -from "$FromName <$FromAddr>" -cc "$CCName <$CCAddr>" -subject "Please Logout" -body "please logout body" -smtpServer $SMTPServer
}