What he said: my Crown graphic can go from packed to shot in 30 seconds, including a flash charge (assuming the batteries are fresh).

On the other hand, I would recommend you think about what you are trying to shoot. If you are seriously trying to do landscapes, you can't beat a field camera (and you can use a roll film back on most, if you really want to). Taking an extra minute to set up the camera and think about what you are doing is not the end of the world.