There's a lot of data to support sleep debt theories, but there's also lots of data that throws these theories out the window.
In high school, I would go to bed at 2-4AM and wake up at 6:30-7:30AM without fail. No alarm clock needed, and I was never late for school. I never felt bad about it, never had trouble focussing, got straight As and even had time to write two novels in the time that I spent not studying (and I didn't study or revise, so that was just about all the time). One thing I did notice though, if I stayed up for at least 30 hours I would stop having useless thoughts (mental state akin to meditation) and my mathematical abilities became extremely refined (e.g. Being able to multiply or divide huge numbers or solve complex equations in an instant, literally). The longest I ever stayed up was around 85 hours, however this trait remained consistent the entire time.
In college (studying the IB), I would go to bed at 12-1AM and wake up at 6:30AM on the dot, every day. I actually used an alarm during this time because I had to travel a long way each day and would get an extra 2 hours of sleep on the bus each way (at least when I didn't get disturbed by the 3 all-girl school groups of kids that piled in every morning.... Damn noisy creatures). Arguably this was a much more healthy sleeping pattern, but I didn't notice any difference to only getting 3 hours of sleep. I still did just as well in college.
University was much easier and I could sleep in every day, so no matter when I went to bed, I would get up at 9-10AM. These days I go to bed at 12ish, and wake up any time between 7:30 and 11AM, depending on how my body feels. I still sleep on busses and trains, so maybe I'm getting too much sleep these days. Either way, there is no impact on my mentality or physiology. The only difference is that if I get less than 4 hours of sleep, I get snappy for 40 minutes after waking up. Otherwise my mind is as sharp as ever, and my immune system better than most (before entering high school, I would always have a cold or flu or something, but afterwards I almost never got sick unless it was something major).
Sleep probably depends on the person, so guidelines are useless. Just sleep as much or as little as your body feels it needs.