Our bodies are all different, and the same rings true for our circadian rhythms. Some of us tend to be morning people, able to be wide awake and functioning at the crack of dawn. Whereas some of us tend to be night owls, able to stay up until the late hours of the night (or early morning!). However, when it comes to how much sleep one actually requires to optimally function, the range is not as big.
When calculating what time to go to bed, it really comes down to your circadian rhythm. Individual’s circadian rhythm could differentiate by hours. If two people were to both go to bed at the same time, one could be sleeping at the perfect biological time and the other at an adverse biological time. Unfortunately, the easiest and best way to measure this is by testing melatonin levels through blood or saliva samples. The quality of your sleep heavily depends on the timing of sleep relative to your circadian rhythm. If you sleep at the right biological time, you'll get optimal recovery sleep. However, when you are sleeping at a non-optimal time, the quality of sleep reduces. An extreme example of this is when the circadian rhythm is disrupted, for example when jet lagged or working shift.
Our bodies respond well to routine. If you manage to find a bedtime that works best for you and achieve the amount of sleep your body requires, you might just find yourself waking up a couple of minutes before your alarm is scheduled to go off!