[greg zakharov]

andr_mozg, на JS (без WMI):

Код:

(function() {
  var enc, arr, i, s = '', std,
      loc = {
        419 : ['019', '1251'],
        409 : ['009', '1252']
      };
  
  Array.prototype.to_s = function() {
    var s = '';
    
    for (var i = 0; i < this.length; i++) {
      s += i === 0 ? parseInt(this[i]) + '.'
        : (parseInt(this[i]) < 10 ? '0' + parseInt(this[i]) : parseInt(this[i])) + ':';
    }
    return s.replace(/\:$/, '');
  };
  
  with (new ActiveXObject('WScript.Shell')) {
    enc = Number(RegRead('HKCU\\Control Panel\\International\\Locale'));
    arr = RegRead(
      'HKLM\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\' +
      'PerfLib\\' + loc[enc][0] + '\\Counter'
    ).toArray();
    
    for (i = 0; i < arr.length; i++) {
      if (parseInt(arr[i]) === 2 || parseInt(arr[i]) === 674) {
        s += '\\' + arr[i + 1];
      }
    }
    
    std = Exec('cmd /c chcp');
    i = std.StdOut.ReadAll().match(/\d+/);
    std = Exec('cmd /q /k echo off');
    std.StdIn.WriteLine('chcp ' + loc[enc][1]);
    std.StdIn.WriteLine('typeperf "' + s + '" -sc 1');
    std.StdIn.WriteLine('chcp ' + i + '&exit');
    s = parseInt(std.StdOut.ReadAll().match(/\d+\.\d+/g)[2]);
  };
  WScript.echo([s / 86400, s / 3600 % 24, s % 3600 / 60, s % 60].to_s());
}());

Советую еще почитать в консоли typeperf /?

P.S.Можно uptime получить и на чистом cmd:

Код:

@echo off
  setlocal
    chcp 1251>nul
    for /f "tokens=3 delims=.," %%i in (
      'typeperf "\Система\Время работы системы" -sc 1^
       ^| findstr /rc:"\:"'
    ) do set "t=%%~i"
    set /a "ss=t%%60", "t/=60", "mm=t%%60", "t/=60", "hh=t%%24", "dd=t/24"
    if %hh% lss 10 set "hh=0%hh%"
    if %mm% lss 10 set "mm=0%mm%"
    if %ss% lss 10 set "ss=0%ss%"
    echo:%dd%.%hh%:%mm%:%ss%
  endlocal&chcp 866>nul
exit /b