There are a whole class of patrons that are watch-checkers. I see them just before we open, and just before we close. Most of them wear wrist watches which, evidently, are set every morning, at a minimum, to the observatory at Greenwich, plus eight hours. My clocks are not.
It starts somewhere around 11:58 (we open at noon). The forearm rotates and rises to the eyes, causing their brows to furrow into a frown. I am very aware that their watch says 12:00. The only thing I haven't seen them do is tap their foot and cross their arms. Of course, they can't cross their arms because then they wouldn't be able to keep track of our callous disregard for the exact, and true, time.
Somewhere during the day, the Greenwich Observatory loses somewhere around 4 minutes, because the process is repeated at 9:00 when we close. Not the same people of course (not even my most ardent internet users, usually, stay the full nine hours that we're open). Except now it's worse.
At 8:45 I give a loud, verbal, warning that we are closing in fifteen minutes. I can tell who the watch-checkers are: they check their watches and instead of furrowing, their eyebrows arch in surprise. They're not too worried, however, because it's an approximate warning- certainly couldn't be precise, because the library should be closing in 16 minutes and 37 seconds.
At 8:55 I give the five minute warning. Now they're worried. It should be seven minutes and they are nowhere close to having found that perfect DVD. How can they possibly make a selection with that sort of pressure?