(measure-command{
$first = [datetime]"2000/1/1"
$last = [datetime]"2018/1/1"
foreach($t in 0..($last - $first).TotalHours)
{
$first + [timespan]::FromHours($t)
}
}).TotalMilliseconds


$first + [timespan]::FromHours($t)

Write-Output ($first + [timespan]::FromHours($t))
にすると3倍くらいかかる