In season 1 episode 7: Red in the Face, there was this exchange:
Roger: What are you up to tonight?
Don: I'm on the 5:31.
Roger: Reservations at home. I've had those.
What does the 5:31 refer to? I tried to search its meaning and the closest thing I could find was maybe a reference to Matthew 5:31. I assume it just means what Rogers replied: "Reservations at home", but where did this saying come from and was it used frequently back in the 1960s?
Handy notes that Weiner had his writers research the train schedules in 1960, so when Don says he’s taking the 5:31 to Ossining, that means there really was a 5:31 to Ossining that day.
Slate magazine, AUG 13, 2009
The 5:31 train is probably the first commuter train that you could catch if you left the office at 5:00. It indicates that he intends to leave the office exactly at "quitting time" and head home, which was really frowned upon at the time if you were trying to be upwardly mobile (i.e. get promoted). Most companies expected you to put in extra time, to show dedication.