A couple of clicks, and a few seconds. I usually do it just as I approach my driveway, and by the time the car is in a position where it needs the height, it has already finished raising itself up.
While not instantaneous, the screen makes it quite easy to click, so you can quickly hit raise while driving, for example when you see a surface street with issues up ahead.
Geofenced ride height would be superb, and shouldn't be that onerous to implement. I believe Tesla geofences the on-vehicle charging setup, so you always charge at the same setting at the same location.