Consiglio: If you want to wake up early (or at any specified time), try to fall asleep along an interval of 90 minutes -3/4.5/6/7.5/9 hours- this is how long each REM cycle is. Waking between cycles leaves you refreshed, while waking in the middle will leave you groggy.

Say I want to wake up around 7AM. I also know with my body, I need at least 7 hours of sleep. REM cycles are usually 90min on average. It also takes the average human 14 minutes to fall asleep. The best rest I will get is not going to bed at midnight, but rather near 11: 15PM. I will fall asleep near 11: 30, and get 5 full REM cycles before waking up.

Check out this website if you'd like a webpage that does these bedtime calculations for you (it also shows when you should wake up if you are going to sleep now instead).

I've tried this out and it has helped me to realize my sleep needs and how I can push them. If I was staying up late studying for instance, I'd stay up til later if it meant my REM cycles would line up better than quitting at the moment I wanted and adding an extra half a cycle in. Hope this helps some people sleep better!