This code is test and work in android.
Since after IOS7 IOS can setup the screen mode to "Never"

this.OSName = Ti.Platform.osname.toLowerCase();

if(this.OSName == "android"){  
        this.MainWindow.keepScreenOn = true;
    };

if(this.OSName == "iphone" || thisClass.Parent.OSName == "ipad"){  
   Titanium.App.idleTimerDisabled = true;
   this.MainWindow.idleTimerDisabled = true;
};