Perhaps a too simple question. I know that you press the lock differential button on the dash in my 2004 LC (just bought it used) -- when you want to lock the differential. I've read the instructions - and it just states to press the button to lock the differential. My question has to do with - when can you press it? While in motion? While in drive but stopped? Or do you have to be in park? I would be using it to drive on snow covered roads. Thanks - Mike