PowerTip: How Long Has My Computer Been Running?
Summary: Learn a one-liner Windows PowerShell command to see how long a computer has run.
How can I use Windows PowerShell to find out how long my computer has been running
since last boot up without writing a script?
Use the Win32_OperatingSystem WMI class and the LastBootupTime property,
and then subtract the value of the current date/time that comes from Get-Date:
(Get-Date) – (Get-CimInstance Win32_operatingSystem).lastbootuptime