The boy accompanying Oscar Hammerstein II is a young Stephen Sondheim. He derides Lorenz Hart's line "weighty affairs will just have to wait", which later became a lyric in the song Comedy Tonight from Sondheim's musical A Funny Thing Happened on the Way to the Forum.
When introduced to "George Hill" aka future filmmaker George Roy Hill, Lorenz Hart advises him to focus on friendship versus love. Hill would go on to direct, among other films, Butch Cassidy and the Sundance Kid (1969) and The Sting (1973), two films centered on the friendship between two protagonists.
One of the few feature films that take place within (basically) one set and in extemporaneous time of about one hour of that evening. This film was shot in Dublin, Ireland.
As part of his running dialogue/monologue, Lorenz Hart tosses off the line, "A touch of Larry in the night." This is a reference to a line from William Shakespeare's Henry V, "a touch of Harry in the night," when King Henry V went in disguise to walk among his soldiers before the Battle of Agincourt. The King offered his soldiers a moment of connection with their monarch and a sense of reassurance on the eve of battle. Hart is talking about wandering Manhattan in the night, meeting people.