For a long time in the US (maybe still?), the vast majority of the schedule was set by the local station. Being a member of one of the national networks brought access to a catalog of shows, and a few requirements about the scheduling of shows that the network really cared about. In almost every nationally-produced promo you got the phrase “check your local listings” in addition to the advertised time because the local station might air the show sometime other than when the network recommended.