How to check the system up time
If you want to quickly and easily see how long a server has been running for since its last reboot then use this function:
$os = Get-WmiObject win32_operatingsystem
$uptime = (Get-Date) - ($os.ConvertToDateTime($os.lastbootuptime))
Write-Output "Uptime: $($Uptime.Days) days, $($Uptime.Hours) hours, $($Uptime.Minutes) minutes"