I actually purposely used to set all the various clocks at home ahead by anywhere from 0 - 15 minutes. At first, I could remember which ones were ahead by how much, but then soon I started to forgot and had to just assume they were running at the right time. It worked great.
After a few years of this, I set them all back to right time and found that I had trained myself to just leave at the right time, with no more trickery needed.
I saw an alarm that had a propeller on top of it. The clock made it fly and you had to hunt it down (even if it falls behind the furniture) to shut the alarm.
After a few years of this, I set them all back to right time and found that I had trained myself to just leave at the right time, with no more trickery needed.