ex_m039010m откопал весьма любопытную статейку из Википедии:
Dramas' starting hour
Most Japanese dramas never start exactly on the hour or half-hour mark. Instead, some episodes start at 8:58 p.m., while others start at 9:05 p.m. Before television ratings started to matter, episodes started exactly on the hour. Later, because of the aggressive TV ratings war, some stations decided to beat the competition by starting their shows a few minutes earlier. The theory behind this practice is that when a show ends a few minutes before the hour or half-hour, a viewer would start changing channels until they found one that wasn't showing any commercials. Similarly, if an episode runs a few minutes past the hour or half-hour, viewers are more likely to watch the next program because they missed the first few minutes of an episode on a different channel.
The exception to this trend is
NHK, which continues to start their shows exactly on each hour or half-hour. Potential reasoning behind this is that because every other television station is constantly changing its start times, this strategy no longer holds the potential advantage over competition that it once did.
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Источнег - последний абзац
тут.