Wouldnt hitting "4" and "start" be almost as fast? Unless you eat an absurd amount of butter I don't see how much time it could possibly save someone.

If the cooking is under 10 seconds, you might as well start it for 10 seconds and stop it when needed. You won't have time to turn around and forget about it.

If it's over, I doubt a one-second difference will make one (difference).

True. I forgot that I often hit 30 seconds and then watch the microwave until 15 second have passed (or whatever increment I need).