A Time

Japanese: Ａタイム - えーたいむ

...Secondly, it is the time period during which broadcasting stations schedule important programs such as major news, news programs, and popular entertainment programs. Thirdly, it is the most important time period for commercial broadcasting, mostly called A time, and the unit price of commercials is also high. In the heyday of radio, the golden hour referred to the approximately three hours of radio broadcasting time from 7 p.m. onwards. ...

From [Radio Charges]

…In general, the charges are higher for wide-area stations in metropolitan areas such as the Kanto and Kinki regions, and generally lower for prefectures with smaller populations. As for charges based on time of day, the prime time (7:00 pm to 11:00 pm), which has the highest average viewer ratings, is usually called A time and is the most expensive, followed by B time, C time, and so on. In a broad sense, spot charges are sometimes also referred to as the radio wave charges. …

*Some of the terminology that refers to "A time" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…第2に，主要なニュース，報道番組，人気娯楽番組など，放送局が重要番組を編成している時間帯である。第3に，民放では営業上最も重要な時間帯で，大部分はAタイムといい，コマーシャルの単価も高い。ゴールデンアワーは，ラジオの全盛期には午後7時から約3時間のラジオの放送時間を指した。…