Calculating the Offline Time for a Windows 10 Upgrade

For my Windows 10 feature update installation process, I like to gather lots of statistics around the upgrade itself as well as the devices they are running on so we can later report on these. These stats can be useful for identifying areas of potential improvement in the upgrade process. One stat I gather is the offline time for the upgrade, ie the time between when the downlevel (online) phase is completed and the computer is restarted and the time when the offline phases have completed and the OS is brought back to the logon screen again. Knowing this value across the estate helps to gauge the user experience and how much time is being spent waiting for the offline phases to complete.

To calculate this value is actually straightforward – you can do it by searching the SYSTEM event log for the last time the computer was restarted and comparing it with the installation time of the OS which gets recorded in WMI after the offline phases have completed successfully. The only thing is, after the offline phase is complete the event logs are refreshed and previous log entries are removed, so you have to search the event log in the Windows.old folder instead. You have to do this before the Windows.old folder gets automatically removed (depending on your policy) and manual rollback is no longer possible.

The PowerShell code below searches for the most recent event ID 1074, compares the date with the OS install date value in WMI (use the *CIM* cmdlets to get an automatic conversion to [DateTime]) and outputs as a TimeSpan which you can log however you want.

The good news is that for a 20H2 upgrade from media – at least in my various tests – the offline time has been impressively low.

$Params = @{
    Path = "$env:SystemDrive\Windows.old\Windows\System32\winevt\Logs\System.evtx"
    Id = 1074
$LatestRestartEvent = (Get-WinEvent -FilterHashtable $Params -ErrorAction SilentlyContinue | Select -First 1)
$InstallFinishedDate = Get-CimInstance Win32_OperatingSystem | Select -ExpandProperty InstallDate
If ($LatestRestartEvent)
    $UpgradeOfflineTime = $InstallFinishedDate - $LatestRestartEvent.TimeCreated