Interesting, would be a kinda silly to have them preheat even if you don't intend to drive ...They start preheating when you unlock/open the door. Like your Idrive starts to boot up before you push the start button.
In almost all cases my 335D will start immediately on the button.
I'm with tlak and Grentz on this one. The glow plugs don't light up the moment the door is opened. The glow plugs are of the quick heat variety. If more than a quick glow is required, then there is a delay in when the engine turns over after the Start button is pressed.Interesting, would be a kinda silly to have them preheat even if you don't intend to drive ...