I'm unclear as to the "auto off timer" that this product has. The manual just says to "press and hold the start button until the timed grinding cycle is complete, about 15 seconds for 12 cups." Does the machine stop automatically? Mine doesn't. What if I have only 4 cups to make, will the grinder grind for less than 15 seconds? My grinder never goes off alone, and I'm wondering what this "auto off timer" is.