This is utterly fascinating. Note the quotes about "occupied time":
The basic notion, says MIT researcher Richard Larson, is that time goes by if you are doing something — anything — that occupies you; even if that something is stabbing your finger onto plastic bubbles. "Occupied time" just feels shorter than "unoccupied time." People doing nothing in a line typically overestimate their wait by about 36 percent.
This explains some of the things I've read about queueing theory.