You can use Get-Process
to see when the service process was started, like so:
Get-Process | select name, starttime
This will get the processid based on the service name:
$myservice = "Spooler"
$starttime = Get-Process -id ((Get-WmiObject win32_service -Filter "name=`'$myService`'").ProcessID) | select StartTime
$timerunning = (get-date).Subtract($starttime.StartTime)