Study and Note taking should permit mapping of concepts upon each other so that the revision notes can summarise large amounts of thinking, learning and concentration in a few well chosen words or diagrams. Authorities recommend 8 hours a day for most people. Forget the advice of Napoleon. 6 hours a day is not enough sleep for most normal men and most women need more than 7 hours. The learning of coordinated physical tasks is particularly impaired by sleep loss, Interventional Radiolgists in-training, take note.
Teenagers sleep at different times from adults.
Their hormonal background often means that they are awake later than normal adults. This need not be a problem, provided that total hours sleeping are at least 8 hours and, ideally, more than 8 hours a day. Students often confuse metaphor for the underlying truth that it is supposed to represent. Most good teachers will, at some stage, make a compromise to obtain brevity and clarity, when trying to elucidate a particular point. The purpose of metaphor and simplification is to provide a skeleton of thinking upon which the neophyte may add the flesh of the greater body of information on the subject being taught.