When Is It? (Historical Character)

In Act 1 Scene 4 it is New Year's Eve 31st December 1929 but when the song 'Telephone Dance' starts it is then after the midnight countdown and is 1st December 1930. The scene is placed in the Kit Kat Klub and I reckon the dance is happening not too long after the New Year has come in so 12:15-12:30. This part of the scene is happening at the tables of the club, the dance floor and bar as when my chosen character the '1st Girl' is rejected by Cliff and goes straight to the bar.