I often find myself needing to convert the LastLogonTimeStamp attribute from Active Directory to Datetime with PowerShell. What I have done, is that in my PowerShell profile ($profile) I have added a function ConvertFrom-LastLogonTimeStamp to get the value as a Datetime.

Easier to remember!

function ConvertFrom-LastLogonTimestamp
{
    [CmdletBinding()]
    [OutputType([datetime])]
    Param
    (
        # LastLogonTimestamp from AD
        [Parameter(Mandatory=$true,
                   ValueFromPipeline=$true,
                   Position=0)]
        [String] $LastLogonTimestamp
    )

    return [datetime]::FromFileTime($LastLogonTimestamp)
}