Rambam contradicts himself. He says 8 hours and wake up with sunrise, but he also says in halakhos deah, I think, that one should learn both day and night, a this is different type of learning. During summer, both are impossible. So, one advise is to maximize health, another – learning.
As different people need different amount of sleep and at different periods of their life, you should experiment: go to sleep at same time daily and wake up without alarm clock. In 1-2 weeks, you’ll stabilize at the hours of sleep that you need.
If you sleep less, you may be forgetting your learning. Basic experiments with mice show that: show a mice a new box, it will go explore it on the first day and ignore on the second as a known object. If you disturb sleep, it explores the box on the second day forgetting what it saw a day before.
There is research comparing pairs of nearby US cities, one at the west end of one time zone, next – at the beginning of the other. One of them gets more sleep, almost an hour on average, also has 10+ on IQ and $10K on income. Whether sleep makes them smarter/richer, or whether smrt/rich people choose to sleep more, it is a good example to emulate. Hope I did not offend anyone on the western side.
Also, try not to get up during deep sleep. Fitbit and similar can measure your deep sleep cycle, usually every 1.5 hours. Teenagers especially should sleep more in the morning. Explain it (respectfully!) to your parents and teachers and tell them you’ll learn better that way. And actually do that.