Open up virtually any health-related magazine, and you're sure to find something in it about sleep, whether just a few sentences, or an entire article. Unfortunately, everything that is written is open for dispute by individuals.
People sleep better without time pressure.
Actually, I find consulting the clock a pleasure during the night. If I have still an hour of sleep before I wake up, it is a delight to go back to bed and know that I get one more hour of blissful rest. I realize that some people will have the opposite reaction. And herein lies the problem. Sleep is a very unique activity.