Modifique seu Get-WinEvent
com um filtro.
$startTime = get-date "5/22/2012 20:00:00"
$endTime = get-date "5/23/2012 11:00:00"
Get-WinEvent -FilterHashtable @{Logname="System"; StartTime=$startTime; EndTime=$endTime} | Export-CSV -Path c:\temp\output.csv