A convenient forumal which covers a great deal is, "Culture is the organization of daily life." (I originally got this from Louis Kampf: I don't remember whether in his book or in conversation.) In the United States daily life is dominated, above all, and for almost the whole population, by the clock. This is true not just of work time but of almost every instant of the day. For one huge sector of the public, evening hours, including the evening meal, will be organized around the TV schedule. Almost certainly this organization of the viewers' time is more culturally and ideologically important that the ever-changing content of what is watched. That is one reason it is possible to study the cultural impact of TV without attending to any of the actual TV shows.
Up until some time in the '50s movies were less structured by time: One went in at any point and viewers divided into those who left when they reached that point in the next showing and those who stayed through till the movie's end. Now of course, with a definite intermission, movies structure time as rigidly as does TV or radio. TV (and formerly radio) structure the time of the whole household, not just those who are watching/listening. My grandfather was a news addict (radio), and that determined which part of the evening one could talk and which part one had to be still. (We lived with my grandparents while my father was in the TB San.)
In schools, of course, the class length is determined by the clock, not by the topic. This is just one of tha many irrationalities of capitalism.
Analysis of culture must start with and be dominated by this organization of human activity by the clock. No other element in human life (currently) is as culturally important as the cljock.
Carrol