They also break the 'fourth wall' there. The Showa Era was from 1925 to 1989, then the current Heisei Period began. It was also when early plasma screens began replacing 'picture tubes' in TVs. All that from +/- 10 seconds of dialogue.
@07:50- the 3rd girl introduces herself as Haruo Minami (三波春夫,1923 – 2001). He was an enka singer in postwar Japan. He sang the close for 'Super Zugan,' a popular anime that aired in 1992 on Japanese TV.