Get the last time app pool was Restarted.

Get-WebAppPoolStatus.ps1

function get-webApppoolstatus($pool)
{
    $poolReturn = @()
    $poolStatus = gwmi win32_process -filter "Name like '%w3wp%'" | select name, Processid, commandline, creationdate
    #$poolstatus.converttodatetime($poolStatus.creationdate)
    foreach($status in $poolStatus)
    {
        if(($status.commandline) -like "*$pool*" -and ($pool -ne $null))
        { 
            $status.creationdate = [System.Management.ManagementDateTimeConverter]::ToDateTime($status.creationdate)
            $poolReturn = $status
        }
        elseif($pool -eq $null)
        {
            $status.creationdate = [System.Management.ManagementDateTimeConverter]::ToDateTime($status.creationdate)
            $poolReturn += $status
        }
    }

    return $poolReturn
}