I used to think it was Detour, but after seeing My Name is Julia Ross on TCM last night, I have since changed my mind. Any others I am overlooking?
Definitely the 73 minute Cat People.
Duck Soup. 68 minutes and one of the greatest screen comedies ever.
Primer clocks in at 77 minutes, but I think deserves a pass - for an indie made for $7,000 a couple of years ago, it has been hailed as one of the great movies to use time travel to explore big questions - and is damn thrilling, too.
End credits don’t count- surely this had at least three minutes of them 
In the realm of B&W horror flicks, is it better than the 71 minute Frankenstein or the 75 minute Bride of Frankenstein?
Can I nominate this ?
There’s the 28-minute La Jetée:
Buster Keaton’s Sherlock Jr. (44 min.)
Disney’s Dumbo (64 min.)
Ulmer’s The Black Cat (65 min.)
Buster Keaton’s The General is 74 minutes. I think it deserves a pass, too.
Oh, I guess The General doesn’t NEED a pass, since it’s less than 75 minutes. I was thinking the OP said less than 70 minutes.
But I would petition for a pass for Nosferatu (1922, 84 minutes) and, really close, The Passion of Joan of Arc (1928, 77 minutes).
• Another Val Lewton movie, I Walked With a Zombie.
• Harold Lloyd’s Safety Last! (1923).
• The Last of the Mohicans (1920).
• Rudolph Valentino in The Son of the Shiek (1926).
• Freaks (1932).
• Mae West in She Done Him Wrong (1933).
• W.C. Fields in The Bank Dick.
• The Ox-Bow Incident (1943).
The Emperor’s New Groove
I just looked at the plot summary you linked to, and the setup is almost identical to Twin Husbands --except the protagonist is male in Husbands. Interesting how Hollywood reused plots over and over again.
Speaking of Val Lewton, *The Leopard Man * (1943).