@echo off & setlocal enableextensions
  call :GetDateTimePS start_
  echo Whatever ...
  pause
  call :GetDateTimePS endat_
  call :TimeDiffPS "%start_%" "%endat_%" elapsed_
  echo Start at "%start_%"
  echo Ended at "%endat_%"
  echo %%elapsed_%%=%elapsed_%
  endlocal & goto :EOF

  :: The indentation is essential to avoid incorrect syntax
  :GetDateTimePS
  setlocal
  for /f "usebackq delims=" %%A in (`powershell -NoLogo -NoProfile -Command ^
    "Get-Date -Format 'dd.MM.yyyy HH:mm:ss'"`) do (
      set "result_=%%A")
  endlocal & set "%1=%result_%" & goto :EOF

  :TimeDiffPS
  setlocal
  for /f "usebackq tokens=1-3 delims=" %%a in (`
    powershell -NoProfile -Command ^
      "$a=[datetime]::ParseExact('%~1','dd.MM.yyyy HH:mm:ss',$null);"
      "$b=[datetime]::ParseExact('%~2','dd.MM.yyyy HH:mm:ss',$null);"
      "($b-$a).ToString()"`) do (set result_=%%a)
  endlocal & set "%3=%result_%" & goto :EOF