The strange thing is that I usually can wake up about 5 minutes before whenever I need to wake up. When I was sailing we’d have watches (like shifts not rolex) that would rotate through the day. One watch you’d have 3 hours to sleep and have to be up at 7pm, then the next watch you have 6 hours to sleep and have to be up at noon… that kind of thing. Never had a problem with it.

Still, when I need to be up for something important, I chicken out and set my alarm anyhow.