Here’s a quick and easy way of checking how long a Windows server or workstation has been up, via the command line.  It pipes the results of Net Statistics Workstation into find.  Run the following from a command prompt:

net statistics workstation | find /i "statistics since"

The results will look like

Statistics since MM/DD/YYYY HH:MM PM

Which shows the machine has been up since 02:45 pm on September 9th, 2017.