not exactly true. the same studies said that youre supposed to get up, drink some water, go to the bathroom, or do whatever for a few minutes, then go back to sleep to get the benefits. so youre sleeping 8 hours its just divided into two nice perfect sleep cycles instead of one long cycle thats all jacked up
and thats not really true either. everybody is different. the best way to find out how much sleep you need is when youre on vacation or on your days off, just sleep until youre not tired anymore, dont use your alarm, do that a couple days in a row, and thats how much sleep your body actually craves and needs