This Rodgers and Hart song was introduced by Benny Goodman, with vocalist Louise Tobin, on the Columbia label on September 13, 1939. It entered the charts on October 28, lasting for 13 weeks and peaking at sixth position. On December 23, Jimmy Dorsey & His Orchestra’s version hit the charts for 2 weeks and rose to thirteenth position.

Around the same time, Marcy Westcott and Richard Kollmar sang “I Didn’t Know What Time It Was” in the Broadway musical for which it was written, Too Many Girls, which opened at the Imperial Theater on October 18, 1939, and ran for 249 performances.

In 1940, Rodgers and Hart wrote the score for another musical, Higher and Higher, which included the song “It Never Entered My Mind.” The lyrics for both of these songs have two things in common: both are examples of the then current trend to use a common expression as the key phrase or song title; and the subject of the lyrics of both songs are said to reflect Lorenz Hart’s alcoholism.

According to Rodgers, Hart would write his lyrics after Rodgers had written the music, whereas Oscar Hammerstein would present the lyrics to Rodgers before the music was written. Getting Hart to write was not often easy. After Hart missed several meetings, Rodgers would sometimes go to Hart’s apartment and start playing the piano in an attempt to coax lyrics from the reticent Hart.

In Listening to Classic American Popular Songs Allen Forte says of Rodger’s music, “This temporal wandering in the tonal space directly corresponds to the confusion expressed in the lyric, ‘I Didn’t Know What Time It Was.’” It is a matter of conjecture, then, whether the confusion reflects Hart’s alcoholism, Rodgers’ tonal wandering, or both.

The successful Broadway musical was ripe for screen adaptation. In the 1940 film, Too Many Girls, Lucille Ball replaced Broadway’s Marcy Westcott, although Ball’s voice was dubbed by Trudy Erwin. A Cuban drummer named Desi Arnaz was recruited from the Broadway cast, and it was on the movie set that Lucy and Desi met.