The brain learns from errors, when you play an instrument and hit the wrong note your brain detects that it doesn’t sound right and makes adjustments to keep you from making the same mistake. When you use the microwave, especially if other people nearby are sleeping the sound it makes when the time runs out is extremely annoying, so your brain learns to sense when the timer is about to run out so you can stop it before it makes the sound. When i use the microwave, without even conciously remembering how much time i set it to, i will go focus on something else and my brain will remind me to go to the microwave when the time is almost up, down to a few seconds of accuracy, even though my concious memory of how long i set it to has an uncertainty of a minute or more. i find this slightly interesting