How to get when a user was added on an ad group

 $username    = "dexter.soreta"            

$userobj     = (Get-ADUser $username -Properties memberof).memberof

$dc          = (Get-ADDomainController).name   

$membershipreport = 

foreach($group in $userobj){

    Get-ADReplicationAttributeMetadata $group -Server $dc -ShowAllLinkedValues |             

    Where-Object {

        $_.AttributeName -eq 'member' -and             

        $_.AttributeValue -eq $userobj.DistinguishedName

    } |            

    Select-Object FirstOriginatingCreateTime, Object, AttributeValue   

}

$membershipreport |

Sort-Object FirstOriginatingCreateTime -Descending |

export-csv "MembershipReport.csv" -NoTypeInformation

Import-Module ActiveDirectory            

            

$username = "janitor"            

$userobj  = Get-ADUser $username            

            

Get-ADUser $userobj.DistinguishedName -Properties memberOf |            

 Select-Object -ExpandProperty memberOf |            

 ForEach-Object {            

    Get-ADReplicationAttributeMetadata $_ -Server localhost -ShowAllLinkedValues |             

      Where-Object {$_.AttributeName -eq 'member' -and             

      $_.AttributeValue -eq $userobj.DistinguishedName} |            

      Select-Object FirstOriginatingCreateTime, Object, AttributeValue            

    } | Sort-Object FirstOriginatingCreateTime -Descending | Out-GridView

source: https://community.spiceworks.com/t/how-to-check-timestamp-of-user-added-to-certain-ad-group/965173/3