I see a general chorus of disagreement in the comments, and have to agree - I wake up before my alarm and the clock is reading 6:42 or something when the alarm is for 6:45. It's not some exotic Lamport clock phenomena or some quote out of Nietzsche's "Human, All too Human" ("Everyone knows from experience how fast the dreamer can incorporate into his dream a loud sound he hears, bell ringing, for example, or cannon fire, how he can explain it after the fact from his dream, so that he believes he is experiencing first the occasioning factors, and then that sound"). We just get good at anticipating our alarms.