This show is set in the 1960s, so why have Virginia's mother use the newly constructed phrase "back in the day"? It's not only not period, but jarringly meaningless (my own prejudice).
shareThere's this thing now, called google.
shareI grew up in the 60s and my mother would talk about "The Olden Days". But "back in the day" doesn't sound like an anachronism to me. I don't even remember her mother saying it, and if i heard it it went in one ear and out the other. Nothing about even registrered on my richter scale..
Remember us, for we too have lived, loved and laughed
Since when is the term 'newly constructed'? The wording may or may not have changed slightly over the decades, but those types of sayings have been around a long time. See Shakespeare for evidence of this.
The 60's is a period time to us, now, but in the 60's it was the 30's and 40's (and earlier) that would have been considered period. Period doesn't reflect a set era of time, it's any time previous to the current one.
So yes, the saying is period and is perfectly okay to be spoken in that way.