it knows what it needs. usually round 8hrs. It will also get used to a certain time u get up and it will wake at that time iv notticed. Like if u get up at 5 for a couple weeks your body will most likely alarm you that its time to get up. (it also depends how tried u are)
It's not your body, it's your mind. When you keep waking up at a certain time (and if you go to bed every night at almost the same time) your mind eventually functions it's own alarm clock in it's mind. This trick usually works if your healthy.
Ideally, when it is dark, your body produces melatonin. Melatonin makes you sleep, so when the light comes out in the morning, your body stops making melatonin, which signals that it's time to wake up.
when its sunrise and my room temperature goes up to like from 70 to 80
When I wake uo and don't feel like fainting in bed anymore.
When I have to pee