Perhaps few aspects of modern American life are as startling to the outsider as the contemporary elimination of the clock as a source of limitations on the possible. In 1989 I moved to New York from Geneva, Switzerland, where many groceries actually closed for lunch and then shut their doors for the day at 6, well before I left work in the evening. My Swiss friends explained that shopping hours were based on the assumption that men had wives at home to shop for them; working women or male bachelors had to do their shopping on Saturday. (Stores were, of course, closed all day Sunday.) The convenience of living in America, a society where stores are open long hours on weekdays and both days on weekends, was unbelievably liberating.

Then it kept getting better. In the early 1990s enterprising Korean immigrants added the luxury of the all-night greengrocer, where bleary-eyed New Yorkers could drown their thirsts if not their sorrows–and pick up essential supplies, from a sandwich to a bouquet of roses, at the same time. As the nocturnal population of “the city that never sleeps” embraced the 24-hour greengrocers, the supermarket chains realized they could not afford to lose out on this clientele. Today, the sun never sets on the New York supermarket.

Older Americans tell me this is new for them, too. “Sure, you could find a Sunday paper at the corner drugstore, and maybe get a soda pop at the fountain,” one octogenarian friend explained, “but otherwise everything used to be closed on Sunday.” It seems hard to believe today, but America used to be a more religious society, in which the Fourth Commandment’s injunction to observe the seventh day as the Sabbath was taken very seriously, and people went to church or stayed at home. Until the 1960s it was illegal in most American states to sell alcohol on a Sunday. But that, as Americans like to say, was then.

Declining religiosity in public life is hardly a particularly American phenomenon, though in Europe it is still uncommon to find shops and pubs open on a Sunday. (An entirely random sample poll I conducted among 10 Americans of my acquaintance revealed that none of them could identify the Fourth Commandment. “You’re sure you don’t mean the Fifth Amendment?” one asked me.) But there is a larger phenomenon at work here. Americans are constantly testing the man-made limits to their freedom to engage in their fabled pursuit of happiness. Where others accept that some things are simply not possible, or not done, at certain times or on certain days, Americans ask, “Why not?” In America, someone is always willing to do it, for the right price, at any time. Have an urge to practice your golf at 2 a.m.? There are computerized driving ranges open at that hour.

This trend dovetails perfectly into the increasingly 24/7 nature of American life. Technology has ensured that Americans are always connected, all the time–by phone, e-mail, pager, answering machine, BlackBerry or message service. A hundred years ago, sociologists studying American affluence developed theories of the leisure class, an elite segment of society; today the time has come for a theory of the always-on-call class, a majority of society. There is no longer any real break from the insistent demands of American life. After all, you can always be reached on a Sunday; you can retrieve messages when you are on vacation; you can answer your e-mails from a laptop on the beach. You’re always connected, always on call.

No wonder you need grocery stores that are open all night. You’re single, or divorced, or in a relationship in which both of you are working; how can you shop during your ever-longer office hours? If you need money, there’s an ATM down the street where you can get some at any hour of the day or night (if you’re willing to risk being mugged). If you want to talk, there are nocturnal radio call-in shows where you’ll always find a host willing to let you vent your spleen. If you’re bored, there are at least 35 television channels to choose from at 3 a.m., and you can always go onto the Internet, that ultimate exemplar of the 24/7 society, to conduct an intimate chat with a stranger who could be halfway across the world, or next door.

In America, it simply no longer matters what the time is.

is the author, most recently, of the novel “Riot.”